Aaron Glenn has a pretty good idea what Terrion Arnold will bring to the Detroit Lions defense this season, but the Lions' fourth-year defensive coordinator stopped short of saying Arnold will start at cornerback Week 1 if his training camp is over because of his chest injury.

"I can’t say that," Glenn said Wednesday in Allen Park. "We’ve got to see what happens."

Arnold left practice Monday with what the team termed an upper-body injury and did not take part in Wednesday's workout, when he spent the early part of practice working on the side in a rehab group with trainers.

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Lions coach Dan Campbell downplayed Arnold's injury in a radio interview Wednesday, and while the rookie is not expected to miss time in the regular season, it's unclear if he will play in Saturday's preseason game against the Kansas City Chiefs or next week's exhibition finale against the Pittsburgh Steelers.

Arnold has worked extensively with the first-team defense this summer, and Campbell said on WXYT-FM (97.1) the Lions' first-round pick was having "a good camp" before his injury.

Carlton Davis, the Lions' other projected starting cornerback, is out with a hamstring injury but expected back for the Lions' Sept. 8 opener against the Los Angeles Rams, and rookie second-round pick Ennis Rakestraw also left Monday's practice with an ankle injury. Kindle Vildor and Khalil Dorsey took most of the first-team cornerback reps Wednesday.

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Arnold is expected to play a key role in the Lions' revamped secondary this fall and winter. He excelled in man-to-man coverage in college and excelled in spring workouts after the draft, though Campbell has said he and the rest of the Lions' defensive backfield need more time together to get ready for the regular season.

That has been hard to come by because of a slew of injuries. Along with Arnold, Davis and Rakestraw, safety Brian Branch did not practice Wednesday, and cornerback Emmanuel Moseley is out indefinitely with a torn pectoral muscle.

Glenn said both Arnold and Rakestraw have the mindset to be impact players as rookies.

"Defense is all about attitude and those are the types of guys we try to recruit on this team," Glenn said. "And you see the different personalities, like you take T.A. T.A. talks a lot, but he has that mentality to go out there and play man coverage. Ennis doesn’t talk a lot, but you see that dog in him. So the thing is, to the core of those guys, they’re the same, but they’re just different personalities. But attitude has everything to do with defense.”

He said he's comfortable with what Arnold has shown so far, even if the rookie remains a work in progress.

"From college, we know he can go out there and play man coverage," Glenn said. "I mean, you go out there and play in any Nick Saban defense (at Alabama), you’ve got to be able to do that, so it kind of compares to what we do. So yeah, we’ve seen enough, but he’s not where he needs to be yet. He has a lot of improving to do, and man, once he comes back from this injury, he’s got to get out there and get on the grind and continue to work.”

Contact Dave Birkett at dbirkett@freepress.com. Follow him on X and Instagram at @davebirkett.

This article originally appeared on Detroit Free Press: Lions' Terrion Arnold no lock to start Week 1 if injury lingers