TORONTO -- When the Red Sox begin a three-game series in Detroit on Tuesday, there's a chance that veteran first baseman-outfielder Mark Kotsay will be on the active roster for the first time this season.

Kotsay is in the final stages of a rehab assignment for Triple-A Pawtucket. The Sox will evaluate the left-handed hitter's progress during Monday's off-day to determine whether he is ready.

"I think he's doing well," said Red Sox manager Terry Francona. "No setbacks, he's showing some good bat speed, he's playing all over the place. He's doing all right. He's starting to sound like he's getting a little antsy, which is good. I'm sure that means he's getting closer."

The original plan was for Kotsay -- who underwent back surgery in late January -- to join the Red Sox around May 1. But a strained left calf prolonged his rehab.

Is Tuesday realistic?

"Yeah, but let's see where we're at," Francona said. "What we don't want to do is set a date and then ... if he's ready, we'd like to have him. I think he knows that. But doing it before he's ready doesn't work."

With Rocco Baldelli currently experiencing some left hamstring difficulties -- which appear to be related to the excessive muscle fatigue disorder that kept him off the field for a large portion of 2009 -- Kotsay's return should solidify Francona's bench.

But Kotsay's mere presence also means more than you would expect from a utility player.

"He's got a lot of leadership on this team," Francona said. "For a guy that comes in new, he's kind of as advertised. Everyone talked about what a great guy he is and he lived up to that."