As expected, Jason Bay will be sitting out the series opener against the Yankees due to a hamstring strain suffered over the weekend. However, in an unexpected turn, filling in for Bay in left is Kevin Youkilis.

Youk, who has spent the 2009 season bouncing back and forth from first base to third base due to injuries to Mike Lowell, will be slipping on his third different mitt of the season as he ventures out to Yankee Stadium’s left-field grass to take on the first-place Yankees.

The switch shouldn’t be too difficult for the swift-fielding six-year veteran as Youk played 18 games in left during the 2006 season — starting 17 of them. In 134 innings in left, Youk has had 39 total chances, making 36 putouts and notching three assists for a perfect fielding percentage.

Rocco Baldelli, the Sox’ fourth outfielder, is heading to the disabled list after fouling a ball off his ankle during batting practice according to Terry Francona. Rookie Josh Reddick has been activated from Triple-A Pawtucket.