An MRI on Cliff Lee's oblique injury confirmed the original diagnosis while branding it a Grade 1, or mild, strain, Phillies general manager Ruben Amaro Jr. said Friday.

"That's exactly what we thought it was," Amaro said.

What the Phillies don't know yet is exactly when Lee will return.

The Phillies placed Lee on the 15-day disabled list last Saturday, three days after he'd pitched 10 shutout innings in an eventual 1-0 loss to the Giants in San Francisco. Lee said he'd felt some soreness after a 10th-inning pitch.

He'll be eligible to come off the DL when the Phillies visit NL East leader Washington next weekend.

"He seems to be doing better and better every day," Amaro said before the Phillies opened a four-game series against the Chicago Cubs at Citizens Bank Park. "We don't know what the timetable is but he seems to be feeling better each day. Hopefully, he'll only miss a couple of starts but we'll see how it goes."

In three starts this season, Lee has compiled a 1.96 ERA while striking out 18 in 23 innings. He's walked only two and given up 14 hits. Thanks to the often punchless Phillies offense, however, he's 0-1.

As badly as they want him back, especially after Kyle Kendrick's disastrous showing in Lee's place Monday in Arizona, the Phillies have to be cautious, Amaro stressed.