(CBS) In the first significant step of Cubs left-hander Jon Lester’s recovery and rehab from left lat tightness and what the team has also termed general shoulder fatigue, the plan is for him to throw a bullpen session Friday in Philadelphia, 670 The Score’s Mark Grote reported.

Lester was placed on the 10-day disabled list last Friday, a day after leaving a start in the second inning of a loss. The Cubs have maintained that he’ll return this season and were optimistic he’d only miss a few starts. He played catch Wednesday ahead of Chicago’s game at Cincinnati, then had his bullpen scheduled.

“His arm is tired,” president of baseball operations Theo Epstein said last week. “That is understandable if you look at the load he has carried over the past two years pitching in seven-month seasons. There comes a time when all pitchers need a breather. This is his time.”

Lester is 8-7 with a 4.37 ERA and 1.27 WHIP on the season. Left-hander Mike Montgomery has taken his spot in the rotation and starts at Cincinnati on Wednesday night.

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