(CBS) As part of a series of roster moves Tuesday, the Bears promoted receiver Rashad Ross and defensive back Isaiah Frey from the practice squad to the 53-man roster.

In corresponding moves, Chicago released running back Shaun Draughn, receiver/returner Chris Williams and tight end Matthew Mulligan. The moves come as the Bears are dealing with a string of injuries on both sides of the ball after Sunday night’s win against the 49ers.

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Ross spent training camp this season with the Redskins but failed to make their roster. He spent time on the practice squads for the Chiefs and Titans in 2013 but has yet to appear in an NFL regular-season game.

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Frey was cut in late August by Chicago after failing to make the 53-man roster. Frey appeared in all 16 games for the Bears in 2013, primarily in nickel and dime packages, recording 37 tackles, so he’ll have plenty of experience in the team’s defensive system.

Williams was active against the 49ers but didn’t record any statistics. The Bears originally acquired him off the Saints’ practice squad in December 2013, but even with the returner job up for grabs after Devin Hester’s and no one taking a stranglehold on it, Williams couldn’t distinguish himself.

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Draughn hadn’t distinguished himself as a reserve behind Matt Forte, and he made a big special teams blunder Sunday when his man blocked an early Bears punt.