DENVER (AP) — Broncos rookie quarterback Drew Lock suffered a jammed right thumb Monday night in a preseason game against San Francisco. The second-round pick said his X-rays were negative as he wore a protective brace following Denver’s 24-15 loss to the 49ers.

Lock throws a pass during the second quarter. (Photo by Justin Edmonds/Getty Images)

There was no immediate timetable for his return.

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“I’m definitely going to be careful,” Lock said. “At the same time, the competitive side of me wants to get out there and keep proving myself to these coaches and to my teammates. … I feel like we’ll make a good decision.”

Lock’s injury happened early in the third quarter, when he was tripped up by 49ers strong safety Marcell Harris on a second-down play. He landed on his thumb as he attempted to pitch the ball to a receiver.

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Drew Lock on Monday night (Photo by Dustin Bradford/Getty Images)

On third down, Lock tried to throw a deep pass but experienced a little bit of discomfort. He went to the bench and the thumb began to stiffen up, leading to him being replaced by Kevin Hogan on Denver’s next possession.

Lock finished 7 of 12 for 40 yards before leaving. He also scrambled twice for 11 yards.

Lock is in contention for the backup spot to Joe Flacco.

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