ALLEN PARK — The Lions were counting on cornerback Chris Houston this season, but he’s still dealing with medical issues from last year. 

Lions general manager Martin Mayhew said on Monday that he wouldn’t rule out surgery for Houston, but he doesn’t really know at this time.

Houston didn’t participate in voluntary minicamp a few weeks ago because of the unspecified injury.

“I think the longer it goes, the more concerned you get,’’ Mayhew said. “Something happened in August, November that we’re still dealing with. There’s a concern there, we’ll see what happens.’’

Mayhew said in February he expected Houston to bounce back from last season when he struggled. Coach Jim Caldwell was more hesitant about Houston two weeks ago.

With so many questions at the position the Lions could draft a cornerback in the first round with their 10th overall pick. Justin Gilbert (Oklahoma State), Darqueze Dennard (Michigan State) and Kyle Fuller (Virginia Tech) are the top candidates.

“The most important thing to me is competitiveness,’’ Mayhew said. “You’ve got to have that guy who doesn’t want any guy catching any balls on him in practice, in walk-throughs,  whatever.  We’re looking for a guy that has that mentality.’’

Cornerback is a position full of questions since there are three young corners who are relatively untested. 

Mayhew issued a challenge of sorts to those three  — Bill Bentley, Chris Greenwood and Jonte Green. Each is entering his third season with the Lions.

“I think the important thing is are they on the right trajectory? Are they showing progress every single year? Are they improving? Some guys walk in from Day One and they’ve got it. They just step on the field, they’ve got it,’’ Mayhew said. “Some guys take a year, some guys take two years.

“It doesn’t take more than three years it doesn’t. If you don’t have it in three years, you don’t have it. This is a big year for those guys,’’ Mayhew added.

“This is a big year to see where they are, I like what I’ve seen this far, we haven’t seen a whole lot. Those guys should develop and should be good players for us.’’

All three were drafted in 2012 — Bentley in the third round, Greenwood in the fifth, Green in the sixth.

Last year they drafted Darius Slay in the second round. He progressed last season, but it’s unclear if he’s ready to be a starter week-in and week-out.

The Lions have eight picks in the NFL draft which starts at 8 p.m. Thursday. 

(Follow @PaulaPasche on Twitter. Order her book,  “100 Things Lions Fans Should Know & Do Before They Die’’ here. It’s also available at bookstores.)