ARLINGTON -- The Rangers are going to be without closer Frank Francisco for a short but indefinite period because of some soreness in his right shoulder.

Francisco was examined by Rangers team physician Keith Meister and underwent an MRI on Monday. The diagnosis was biceps tendinitis and normal soreness, and Francisco received an anti-inflammatory injection.

The closer said it wasn't serious.

"There's no pain," Francisco said. "My arm was just really sore for a couple of days. They gave me an extra couple of days to rest. I'll stick with the program and do what I have to do to get back."

There are no plans to put Francisco on the disabled list, but he is not expected to pitch against the Mariners during the three-game series at Rangers Ballpark in Arlington. Instead, Francisco will try to play catch on Wednesday and have a side throwing session on Thursday.

"We can't rule it out," Rangers general manager Jon Daniels said of the disabled list. "But right now, we're going day-to-day and see how Frankie progresses."

The Rangers will let Francisco take a few days off and see how he responds to rest and treatment. C.J. Wilson will likely be the Rangers' closer during Francisco's absence.

Francisco has nine saves this season, the most in the American League and tied for the Major League lead. He has not allowed a run in 14 appearances, and opponents are hitting .137 off him, the sixth lowest average against a reliever in the American League. His 14 consecutive scoreless appearances to open the season are a club record.

"Obviously, he's a big part of what we're doing," Daniels said. "If he ends up missing a few days, we'll try to get by. We have confidence in a lot of guys in our bullpen. If it's longer than that, it's something we'll have to deal with."

Francisco hasn't pitched since last Wednesday, when he threw 23 pitches in a save against the Athletics in Oakland. It was his third straight game and fourth time in five games that he was used. But Daniels said Francisco might have caused the problem by doing too much in one of his pregame workouts.

"On good teams, the closer is going to pitch three days in a row," Daniels said. "I expect he will again. I'm not worried about that. They may have to watch his workouts and how he prepares for a game. This is a high-intensity role."