The Philadelphia Phillies placed left-hander Cliff Lee on the 15-day disabled list Wednesday with a mild left elbow strain.

The Phillies said DL will retroactive to May 19.

Lee underwent an MRI on his elbow Tuesday in Philadelphia that revealed the strain. He experienced soreness in the elbow after his last start on Sunday against the Cincinnati Reds.

Lee might be able to return as soon as he is eligible to come off the DL, general manager Ruben Amaro Jr. said late Tuesday night, according to ESPN.com.

"It's never good news when you lose one of your No. 1 pitchers, but it's pretty mild," Amaro said.

Amaro didn't offer a timetable.

"We just don't know yet," he said. "It could be two weeks. It could be three weeks. It could be four weeks. Who knows. It could be 30 weeks. We think it will be shorter. It's a pretty mild strain. ... We just have to be really cautious with him."

Lee, 35, is 4-4 with a 3.18 ERA in 10 starts this season. This will be Lee's fifth career DL stint and first since April 19-May 8, 2012 (left oblique strain).

Lee pitched 6 2/3 innings in a win over Cincinnati on Sunday. He said his elbow began to bother him after he threw a career-high 128 pitches in an 11-hit, complete-game loss against the Braves on April 16.

"After the game it was pretty sore," Lee said. "We started doing some treatment on it and it acted like it was doing a little better, and this past start I started feeling it the last couple of innings just about every throw, and obviously it was pretty sore the next day.

"It was definitely concerning that it was there on every throw. With as much season as we have left, I didn't feel that I could keep pitching."

To fill his spot on the roster, the Phils recalled outfielder/first baseman Darin Ruf from Triple-A Lehigh Valley.

Ruf is batting .265 with three doubles, one home run and two RBI in nine games for Lehigh Valley. He missed the first month of the season after suffering a left oblique strain during spring training.

In 85 career games with the Phillies, the 27-year-old Ruf has batted .257 with a .348 on-base percentage, 13 doubles, 17 home runs and 40 RBIs.