Sizemore last played 100 games in 2009 (109). I really doubt he will be an effective MLB player at this point. You rarely see players who have been out that long make an impact. It is a shot in the dark by the Red Sox. They have big money to spend so its no big loss to them if he doesn't comeback.
Nice details in this article. Looks like the Sox medical team came up with a plan to improve his workout regimen and that's what sold him....
HOW GRADY SIZEMORE FINALLY LANDED WITH RED SOX