The Red Sox designated Kotsay for assignment last week after making a trade for Adam LaRoche. Anderson, who at 27 is six years younger than Kotsay, was optioned to Triple-A Charlotte last week after hitting .238 (44-for-185) with two homers and 13 RBIs in 65 games.
Although Anderson -- a right-handed hitter -- will likely factor into the mix at Fenway at some point this season, the club sent him to Triple-A Pawtucket as soon as the trade was completed.
"He's very athletic," Red Sox manager Terry Francona said of Anderson. "Defensively, he's very gifted. He was a very high Draft selection. Got to the big leagues with a lot of fanfare and it didn't work [out] right away. I think that it gives us certainly some insurance in the outfield, especially defensively."
Meanwhile, Kotsay, who was caught in a roster squeeze in Boston, is back in the Major Leagues, much to the delight of Francona.
"And on the flip side, Kotsay is back in the big leagues, where he belongs," Francona said. "I hope he never beats us, but I'll be rooting for him, other than that."
The Red Sox included an unspecified cash consideration in the transaction to help cover part of Kotsay's 2009 salary of $1.5 million.
Rocco Baldelli is currently Boston's only reserve outfielder. However, the Red Sox now have options in the Minors in Anderson and Chris Duncan, who was acquired from the Cardinals last week for Julio Lugo.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.