Emmanuel Moseley's season is Thomas Caldwellover, and the Detroit Lions are once again dealing with depth issues in their secondary.

Moseley, one of four key additions to the Lions' defensive backfield this offseason, tore the ACL in his right knee in his Lions debut Sunday against the Carolina Panthers, ESPN reported.

Moseley was returning from a left ACL tear he suffered last October in a game against the Panthers while with the San Francisco 49ers. He did not play in the season's first four games after undergoing a clean-up procedure on his left knee this summer and pulling his hamstring in his return to practice in September.

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Lions coach Dan Campbell said Sunday that Moseley's non-contact injury "certainly didn't look good," and that Moseley would undergo an MRI on Monday to determine the extent of the injury.

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Moseley was hurt on his second snap of the game, when he planted while following a Panthers receiver in coverage.

The Lions lost starting safety C.J. Gardner-Johnson, another one of their top free agent additions, to a torn pectoral muscle in Week 2. Gardner-Johnson underwent surgery in late September and could make a late-season return.

Cam Sutton, the Lions' third major defensive free agent addition from spring, and Jerry Jacobs have started all five games at cornerback this season, but Moseley's injury leaves the Lions without a proven backup.

Rookie defensive back Brian Branch missed Sunday's game with an ankle injury and his status for this week's game against the Tampa Bay Buccaneers is uncertain. Will Harris played in sub packages in Branch's place against the Panthers. Undrafted rookie Steven Gilmore did not play a defensive snap.

Harris could serve as the team's No. 3 outside cornerback once Branch returns.

"Will’s somebody we’ve got a lot of trust in," Campbell said last week. "He’s banked a lot of nickel reps. And there again, Will, not only to be able to play nickel, outside corner, safety in a pinch, he’s just got so much versatility for us. So that’s good."

Contact Dave Birkett at [email protected]. Follow him@davebirkett.