Allen Park — The Lions plan to give All-Pro receiver Calvin Johnson his first chance to play in the exhibition season Friday night against the Jacksonville Jaguars, but coach Jim Caldwell said he’s not sure if defensive end Ziggy Ansah will be available.

Johnson sat the first two exhibition games for precautionary reasons after undergoing knee and finger surgeries this offseason, but he will most likely get an opportunity to show how he fits in the new offense Friday.

“We plan to get him some work this week,” Caldwell said.

Ansah, meanwhile, came off the physically unable to perform list last week, and Caldwell said he’s “not certain” whether the 2013 first-round pick will make his debut.

“The medical staff will look at him,” Caldwell said. “Even though he’s off of PUP, we’re still going to bring him along just according to what he can handle from a physical standpoint, and so we’ll get a sense of that. He’s doing a little bit more in practice. He’ll do a little bit more tomorrow, and then we’ll see what happens come game day.”

As teams usually do in the third exhibition, the Lions will use most of their starters into the third quarter Friday. The first-team offense had only one series against the Browns two weeks ago and just three last week against the Raiders. The starting defense didn’t play much more.

“We plan to take them through the typical scenario — it’s not etched in stone — is that your first-unit offense and defenses will go through the half (and) come out after the half because this is the first time they’ve had an opportunity to do that,” Caldwell said.

DBs adjusting

The Lions drew six flags for defensive holding and another for illegal contact in Friday’s exhibition loss to the Oakland Raiders, and Caldwell said the defensive backs need to do a better job adhering to the rules being emphasized this season.

A group of NFL referees visited the Lions and every other team to explain the increased emphasis on those defensive coverages and other penalties in 2014.

“Any time that there’s an emphasis on play, it’s going to take some adjusting,” Caldwell said. “It’s pretty drastic from what we’ve been accustomed to over the last year, what’s being called now. But the fact of the matter is what we have to do is adjust to those. The rules are in place, they’re in place for a reason. What we have to do is make certain we abide by them.”

Caldwell admitted the Lions didn’t do well with the adjusted rules last week. Defensive players will be flagged any time they grab a receiver’s jersey, among other things.

“Are we smiling about it? No,” cornerback Rashean Mathis said. “Can we change them? No. Do we still have to play football? Yes.”

Many coaches and players around the NFL have said they think the extended focus on these calls during the exhibition was a scare tactic by the league and that they won’t be called as much during the regular season.

While Mathis agreed that defensive backs will probably be free to be more aggressive in a couple weeks, Caldwell said he’s not anticipating the referees being any more lenient once the regular season starts.

“We’re going to treat it as if that’s the way it’s going to be called the entire season,” he said.

Williams good with switch

Michael Williams, a seventh-round pick as a tight end last year, made his debut at offensive tackle Friday and looked good, according to Caldwell.

“I’ve been impressed with him,” he said. “First of all, the adjustment that he made from an intellectual standpoint. It’s very difficult to go from a position where you are out in space, running routes, catching passes and blocking some to blocking all the time. Not getting your hands on any ball, it’s a different mindset.”

Caldwell said Williams, who’s listed at 304 pounds after weighing 278 at the combine last year, also had to go through a “psychological metamorphosis” for the position change.

“This guy has done it and he’s done a nice job with it, and he’s getting better every week,” Caldwell said. “The key to it is he has to keep progressing.”

Full of receivers

Several Lions wide receivers have proved worthy of consideration for the 53-man roster so far this year.

Behind Calvin Johnson, Golden Tate and Jeremy Ross, a lock because of his return ability, Ryan Broyles has looked the best in the exhibition games, but the Lions likely will keep five or six receivers. Kris Durham, Kevin Ogletree and Corey Fuller have all flashed potential either in games or during training camp, too.

Caldwell listed his expectations for receivers Monday.

“The ability to catch it, block, understand your assignments thoroughly, understand how to deal with spatial awareness in zone, be able to create some space when they’re in man-to-man and obviously be a little versatile, too, because oftentimes you don’t play in the same spot all the time,” Caldwell said.

Extra points

… Safety DeJon Gomes (neck) missed practice Monday.

… Rookie wide receiver TJ Jones (shoulder) sat out and remains on the physically unable to perform list.

... The Minnesota Vikings claimed undrafted rookie linebacker Justin Jackson after the Lions waived him Saturday.