FORT MYERS, Fla. -- The competition for the Red Sox's starting shortstop job might have taken a new twist on Friday night, when veteran Julio Lugo left a game against the Yankees after the top of the first inning with right knee soreness.

Lugo was then taken for an MRI, of which results werent expected to be made available until Saturday morning.

"He was complaining of right knee soreness when he went out in the first inning," said Red Sox manager Terry Francona, "so when we got him in [from playing shortstop], we took him out for precautionary measures -- sent him to get an MRI this evening. As yet, we don't have anything from the medical people. We'll probably have something [Saturday]."

Lugo is battling with Jed Lowrie to be Boston's primary shortstop this season.

Both players are having strong springs. Lugo entered Friday 9-for-20 (.450) with two doubles and four RBIs, and Lowrie was 9-for-24 (.375) with two doubles, two triples and four RBIs.

There had been no mention of Lugo having knee problems until he came out of Friday's game.

"He mentioned something to [assistant trainer] Mikey [Reinold] a couple of days ago, but he hadn't been getting treatment or anything like that," Francona said. "You start having the guys dig a little bit, and I think he has been feeling it. We'll know more as we get the results back."