Cubs catcher Miguel Montero began a rehab assignment with Double-A Tennessee as he takes the final steps before returning from a thumb injury that has sidelined him since July 11 and fast-tracked the call-up of Kyle Schwarber.

Schwarber has been so productive that he's made it impossible for the Cubs to send him down once Montero is ready return to the lineup. Over the weekend, Cubs manager Joe Maddon made it clear that Schwarber was sticking with the big club when Montero comes back.

"It would be hard to do that," Maddon told reporters about sending Schwarber down. "We want his bat in the lineup. He's done a nice job behind the plate and shown versatility in the outfield."

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Schwarber might find more time in the outfield just to keep his valuable bat in the lineup. It will be Maddon's challenge to figure out a rotation once Montero can get back behind the plate.

Schwarber continues to swing a hot stick, batting .333 with four home runs, 13 RBI and a team-leading .977 OPS.

(h/t NBC Sports)