Julio Lugo will likely have arthroscopic surgery on his sore right knee Tuesday to determine the extent of the damage there, and could be back on the field in less than a month if all goes well.

The team believes Lugo has a mensiscus tear in his knee, but the severity of the injury is unclear, and this procedure will allow the team to examine the knee from the inside, and potentially repair any damage they find.

"Before we get in there I can't give you an exact timetable, but our expectation is that he's going to be back and available real close to opening day. If he misses time in the season, we're talking days, maybe a week, unless we find something we don't expect to see in there," general manager Theo Epstein said.

Team doctor Thomas Gill will conduct the surgery.

"If when they go in there and there's an actual meniscus injury and they repair it, then yeah, three to four weeks. If there's nothing, it could be even less than that," Epstein said, noting that Jason Varitek was back on the field three weeks after the same procedure.

It was first apparent that something was wrong with Lugo Friday night, when he left the team's game against Baltimore in the first inning. An MRI conducted on Lugo's knee Friday gave some indication that Lugo had a tear, and the team sent the MRI to Dr. Bill Palmer at Mass General Hospital for a second opinion.

"It's a little bit hard to determine the severity, or the lack of severity. But that's why we have Tom. Tom treats the symptoms, not just the MRI, and they're pretty conclusive that something's going on in there," Francona said

The surgery means that Jed Lowrie steps in immediately as the starting shortstop. The surprising Nick Green and infielders Ivan Ochoa and Angel Chavez will compete for the utility spot, unless the team acquires another infielder.

Epstein said that's unlikely, but anything's possible.

"We don't want to go out and make a major move to replace a player who is going to be out for only that short period of time," Epstein said. "That said, with two guys hurting in the middle infield, we're going to keep our eyes open."

Lugo had been having an excellent spring. He showed up in shape and hungry, and was hitting .450 with 4 RBI. He hurt the knee rounding first in a March 7 game against the Tampa Bay Rays.