FORT MYERS, Fla. -- The right half of Boston's middle infield may have received some fine news on Sunday, when the Red Sox learned that Dustin Pedroia had sustained a minor strain of an abdominal muscle, not of his oblique. But the left half of the infield was not so lucky.

Shortstop Julio Lugo may have a meniscus tear in his right knee, and is overwhelmingly likely to have arthroscopic surgery on Tuesday to repair it. Only if Lugo arrives in Boston feeling significantly better than he did this weekend will the Sox forgo an operation.

"It is not definite," general manager Theo Epstein said. "But it is very probable."

Lugo left Friday's Grapefruit League game against the Yankees after complaining of soreness in the knee and underwent an MRI later that night. That test revealed a possible tear of the meniscus, a common injury among baseball players. But the team's medical staff could not determine the severity of the injury without arthroscopic surgery.

If there is a meniscus tear, recovery should take roughly three weeks to a month. If not, it could take less time. But either way, Lugo is flirting with the possibility of missing Opening Day, now only three weeks away.

"I don't think this is going to be a terribly long procedure, but we just don't know," manager Terry Francona said. "That's why we try to be a little careful."

Lugo, 33, hit .268 with 12 steals in 82 games for the Sox last season, missing significant time with a left quadriceps strain. In his absence, rookie Jed Lowrie flourished, driving in 46 runs over half a season.

Those two then entered into a competition for the starting shortstop job this spring -- and Lugo appeared to be winning, hitting .450 with two doubles in 20 at-bats. But in the time it took the Sox to receive Lugo's MRI results, Lowrie became the odds-on favorite to win the job.

The backup situation is a bit less clear. Francona tabbed infielders Nick Green, Angel Chavez and Ivan Ochoa as possible replacements, and it's possible that one of them will receive a chance. Epstein made it clear that he would not look outside the organization for help.

"It's a pretty simple scope, and it's a really simple repair," Epstein said. "We don't want to go out and make a major move to replace a player who's going to be out only for that short period of time."

There is some precedent for Epstein's views. Catcher Jason Varitek sustained a similar injury in August 2006 and missed almost exactly one month. And designated hitter David Ortiz played with a meniscus tear for more than a year, eventually undergoing arthroscopic surgery after the 2007 season.

Lugo, meanwhile, had felt some discomfort for more than a week, though it didn't appear serious until he asked to be removed from the game against the Yankees.

The team's medical director, Dr. Thomas Gill, will examine Lugo again in Boston, then proceed with surgery, barring an unforeseen improvement.

"If, when they get in there, there's an actual meniscus injury and they repair it, then you're talking three, four weeks," Epstein said of Lugo's recovery. "If they get in with the scope and there was very little, then it could be even quicker than that."

Lugo has struggled to meet expectations during the first half of the four-year, $36 million free-agent contract he signed prior to the 2007 season. A strong hitter throughout four seasons with the Rays, he has hit a combined .247 during his two seasons in Boston. He reached base only 29 percent of the time in 2007, and has hit just nine homers in his Sox career. Compounding those offensive issues, he has committed 35 errors at shortstop over his first two seasons in Boston.

Still, his torrid Grapefruit League stats sparked hope that he may have regained the form that saw him hit 40 home runs over his time with the Rays.

"Our expectation is that he is going to be back and available real close to Opening Day," Epstein said. "If he misses time this season, we're talking days, maybe a week, unless we find something that we don't expect to see in there."

Lugo's injury was nearly compounded on Saturday night when the Sox learned that Pedroia had felt some discomfort while taking swings for Team USA in Miami. Pedroia returned to Fort Myers late Saturday for an examination with Dr. Gill, who determined that Pedroia had a lower left abdominal strain -- not a more worrisome pull of his oblique.

Pedroia is likely to miss only days, not weeks, of action.

Boston bits: Clay Buchholz allowed one run in his 3 2/3 innings against the Orioles on Sunday, striking out six. He was ineffecient, needing his allotted 69 pitches to record 11 outs, but still effective. "It's building slowly but surely," Buchholz said. "I don't have a problem with today's outing at all." ... Right-hander Adam Mills, who allowed two runs in three innings on Saturday, has been reassigned to Minor League camp. ... The right ankle that outfielder Jonathan Van Every sprained on Thursday is still "black and blue and sore," according to Francona, and should keep him out of action for at least the first part of this week.