Right fielder Nick Markakis underwent surgery to repair the rectum abdominis (abdominal muscles) on Thursday, according to the Baltimore Sun.

Manager Buck Showalter said that Markakis probably will not be ready to play in a Spring Training game until the second week of the exhibition season. Markakis, 28, hasn't been able to work out this offseason because of the injury, which he previously thought to be a bone bruise sustained during the second weekend in September.

"We feel we have a good time frame to work with," Showalter said. "Nick is a guy that is usually ready in Spring Training in two weeks. He was ready quickly last year. It should be two or three weeks before he is back to normal. What he is usually doing in January, he is going to do in February. We'll probably back off of him with some of the games early on and pick up between the 10th and the 15th [of March]. I expect him to be a full go for the season."

Markakis told the Sun that he could begin walking a mile a day on Friday, then start lifting in three weeks and resume light baseball activities in four or five weeks. He should be "full go" in about six or seven weeks.

Nationals third baseman Ryan Zimmerman underwent a similar operation last year, with the same surgeon, Dr. William Meyers in Philadelphia, and sat out six weeks as a result.

Showalter knew something was wrong when Markakis took himself out of the last game of the 2011 season, against the Red Sox.

"When he had to come out the last game of the season ... Everybody knows Nick Markakis, you know something is really bothering him," Showalter said. "It's something that we thought would heal with rehab from the physical therapy that he was doing. He got to about 80 percent and couldn't get to that last 20 percent. He went to one of the specialists in Philadelphia. I talked to him the last two nights. He stayed overnight last night, and he is back in Baltimore today. We are very positive about him being ready to go."

"Spring Training is what it is," Markakis told the Sun. "I think if I get two solid weeks in at the end of games, I'll be fine. It doesn't take me long to get back in the swing of things. My main concern is just getting my strength back now."

Markakis said that the cause of his pain was a severe injury to the rectus abdominis as well as an abductor injury on his right side. The newspaper report also says that Meyers discovered scar tissue near the torn muscle as well.

"I wouldn't say it has bothered me for years, but the doctor said there has been damage and scar tissue there and that it is possible that I have been weaker down there in my lower half," Markakis told the Sun. "It's a step-by-step process with it, and we'll see, but I'm hoping this can work itself out and I'll get back to where I was."

Markakis has played fewer than 160 games in a season only twice in his six-year career -- his rookie year (147 games) and in 2008 (157). He played 160 games in 2011, batting .284 with a .756 OPS, 15 home runs and 73 RBIs.