ALLEN PARK -- The Detroit Lions could be without their All-Pro return man for a while.

Jamal Agnew underwent medical testing Monday on the knee he injured Sunday against Green Bay. Coach Matt Patricia declined to talk about it Monday, but former NFL team physician David Chao tweeted he fears it's an ACL tear.

Chao, once the head physician for the Chargers, regularly and accurately comments on injuries based on TV replays.

"We're going through and evaluating everything today," Patricia said. "We'll get that report out when we get to it. There's a process that the doctors are going through right now."

Is it possible Agnew's season is over?

"Again, I'm not going to speculate anything until I get information," Patricia said. "I'm not a doctor."

Agnew was a relative unknown when he was taken out of the University of San Diego in the fifth round of last year's draft, but needed little time introducing himself to the league. In Week 2, he returned a punt for a touchdown to help seal a win against the Giants on Monday Night Football, sparking a season that saw him lead the NFL with 15.4 yards per punt return.

He was named first-team All-Pro for it, and tinkered with some offensive duties as well.

This year, he's averaging just 5.6 yards per punt return, and lost his job as the starting kick returner to Ameer Abdullah on Sunday against Green Bay. (In fairness, he's also had a couple nice returns wiped by penalties.) But he's also played more on defense as well, logging almost half the snaps as a slot corner. He has seven tackles, one pass defended and one fumble recovery.

If the Lions do lose him, Abdullah is the natural replacement on kick returns. He started there on Sunday anyway, even before the Agnew injury. At punt returner, Abdullah, Golden Tate and TJ Jones all have experience. Tate's had a lot of success, too, although his import to the offense could outweigh the benefit of having him return punts.

Rookie running back Kerryon Johnson, who returned punts at Auburn, could also be a candidate. He left the Packers game with an ankle injury, but said afterward he could have gone back in if needed.