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05/10/2013 1:05 AM ET

Happ to miss four to six weeks with head, knee injuries

ST. PETERSBURG -- Left-hander J.A. Happ is expected to be out for the next four to six weeks after he was struck in the head by a line drive in Tuesday night's game against the Rays.

Happ suffered a minor fracture on the left side of his skull and a laceration on his left ear. Toronto's starting pitcher also sustained a sprained right knee on the play after he twisted it on his way to the ground.

The injuries could have been a lot worse, and Happ considered himself extremely lucky, but it's still going to take some time before he can resume throwing off a mound.

"Our doctors have said, just because of his knee, probably a week before he starts throwing again," general manager Alex Anthopoulos said. "From that point, just keeping his arm in shape, it's going to come down to how long is it before he's back on a mound.

"If it's not that much time, then we can maybe make a rehab start or two. But he thinks he might be able to start throwing sooner than that. I just told him we're not going to take any chances."

Happ has been advised not to fly for the time being, and he will remain in Central Florida while the rest of his teammates fly to Boston on Thursday night in advance of this weekend's three-game series.

The 30-year-old Happ will continue to undergo evaluations in the coming days but he's expected to be in the clear. When he's able to resume throwing, Happ will begin working out at the Blue Jays' Minor League complex in nearby Dunedin.

Johnson to be out until at least June

ST. PETERSBURG -- Right-hander Josh Johnson is expected to be out until at least the start of June because of soreness in his right triceps muscle.

Johnson hasn't pitched since April 21 but played catch on Wednesday and will now begin the process of working his arm back into shape. It's going to be a gradual process, though, and one that likely will take at least a few weeks.

"He's started playing catch, feeling better," general manager Alex Anthopoulos said. "We're hopeful to get him into a rehab game starting on the 21st. That's not set in stone, but that's kind of the date that we've had."

The timing of Johnson's potential return appears later than originally anticipated. Toronto's No. 4 starter would have been eligible to come off the 15-day disabled list on May 13, and there was some hope that he would be able to return to the big leagues on May 21 when the club needs another starter.

That has now been ruled out, and the Blue Jays will need to search for an alternative either through a trade or in the Minor Leagues. Toronto doesn't need a fifth starter until May 21 because of a pair of off-days next week.

Johnson is 0-1 with a 6.86 ERA in four starts this season. He is eligible for free agency at the end of the year.

Morrow's next start delayed by back spasms

ST. PETERSBURG -- Right-hander Brandon Morrow's next start has been pushed back two days because of spasms in his upper-back area.

Toronto's No. 2 starter was scheduled to pitch on Friday night in Boston, but is now scheduled to go in the series finale Sunday afternoon.

Morrow experienced some discomfort in his back while throwing a side session earlier this week, but the Blue Jays don't expect it to become a major cause for concern.

When asked if Morrow would definitely start on Sunday, Blue Jays manager John Gibbons said, "We think so, no reason not to at this point."

The injury is being reported as minor, but there will still be a level of skepticism about Morrow's availability to pitch in Boston.

The doubts are a natural reaction after previous injuries to Josh Johnson and Sergio Santos were also described as minor, and eventually resulted in stints on the disabled list despite the club's previous claims.

Morrow got off to a slow start, but his effectiveness has increased in recent outings. He last pitched on May 5 against Seattle, and threw eight innings while allowing two runs on three hits and striking out eight.

The eight innings were the most thrown by a Blue Jays starter this season, and Toronto can ill afford to lose him for any period of time. The club is already without Johnson and left-hander J.A. Happ, which has exposed a lack of depth in the Minor Leagues.

Right-hander Ramon Ortiz is scheduled to take the mound on Friday night in Morrow's absence. The 40-year-old is 2-0 with a 2.18 ERA in four games with Triple-A Buffalo, but has thrown only 3 1/3 innings at the big league level in the past two years.

Just how long Ortiz remains with the club remains to be seen. He was chosen for the spot start mostly because the decision had to be made on short notice, and Ortiz was one of the only candidates who had proper rest.

But there's no guarantee that the start will be handed to Ortiz next time through the rotation.

"He's had some success," general manager Alex Anthopoulos said. "In fairness, he does have a two ERA down there. He's been here before. He's had success, he throws strikes. And if not him, you probably go with someone who's maybe a day off his rotation."

The Blue Jays currently have a four-man rotation of R.A. Dickey, Mark Buehrle, Morrow and Ortiz after Ricky Romero was optioned to Triple-A Buffalo Thursday morning. With a pair of off-days looming next week the club won't need a fifth starter until May 21.

Prospect Osuna may need Tommy John surgery

ST. PETERSBURG -- Blue Jays top pitching prospect Roberto Osuna is in danger of requiring Tommy John surgery.

Osuna, who is the club's No. 2 prospect according to MLB.com, departed his last outing with Class A Lansing because of discomfort in his right elbow.

The 18-year-old was later diagnosed with a torn ulnar collateral ligament and paid a visit to renowned surgeon Dr. James Andrews. Surgery hasn't been recommended just yet, but there's a possibility that it will be in the near future.

"Right now they said just to give him a few days and start playing catch," general manager Alex Anthopoulos said. "He's going to throw to 60 feet [today]. Right now it's basically rest and rehab. But there is a scenario if he does have a flare-up again in the next few weeks that ultimately he may need Tommy John."

Osuna ranks just behind promising right-hander Aaron Sanchez on the club's depth chart for pitching prospects. He has a plus fastball that can hit the mid-90s with reportedly very strong command.

The native of Mexico still needs to work on his slider, but all of his skills are very advanced for someone his age. The club may prefer to get the surgery out of the way now so it doesn't have a negative impact on his development during the later stages of his Minor League career.

Osuna was 1-2 with a 3.63 ERA in five games for Lansing this season.

Gregor Chisholm is a reporter for MLB.com. Read his blog, North of the Border, and follow him on Twitter @gregorMLB. This story was not subject to the approval of Major League Baseball or its clubs.