The Red Sox will move Jacoby Ellsbury to left field to replace Jason Bay and play newly acquired Mike Cameron in center, Boston.com reported today.

And Ellsbury wasn’t too happy about it.

“I think he was a little disappointed, a little concerned that it was like a demotion,” said Red Sox manager Terry Francona, who told Ellsbury about the switch about a week before Christmas.

“We explained that it’s not. Again, we’ve got a guy (Cameron) with longer strides. Jacoby can be a force in left, kind of like Carl Crawford in Tampa. We’re going to have an outfield where not a lot of balls hit too much ground.”

Bay was introduced by the Mets today as their new left fielder. The Red Sox today added third baseman Adrian Beltre.

Cameron, signed away from the Brewers, offered to play left field for the Red Sox despite playing three career games there. As a right fielder for the Mets in 2005, he had a vicious collision with center fielder Carlos Beltran in San Diego.

Red Sox GM Theo Epstein said Ellsbury’s future remains in center field.

“We are more than comfortable with Jacoby in center. We just feel that — for now — this alignment puts us in the best position to win games,” Epstein said.

“Both Mike and Jacoby were great about it and said they would do whatever was best for the team. Jacoby knows he’ll still be a center fielder in the long run, and Mike looks forward to helping Jacoby any way he can.”