ALLEN PARK, Mich. (AP) -- The third game of the preseason is usually something of a dress rehearsal, when teams give their regular starters a bit more playing time.

That may not be the case for Detroit star Calvin Johnson.

"I'm not quite certain you're going to see him at all," Lions coach Jim Caldwell said. "There's no guarantees at this point."

Detroit plays at Jacksonville on Friday night. Johnson, who caught 71 passes for 1,077 yards and eight touchdowns last season despite missing three games, did not play in the team's first two preseason games. He has said he would welcome the chance to play this weekend, but Caldwell and his staff seem intent on keeping Johnson under wraps until the regular season starts Sept. 13 at San Diego.

Johnson, who turns 30 next month, has little to prove in exhibition games, and the Lions always do what they can to protect him from wear and tear. Caldwell said there are no injury concerns about Johnson right now.

Other regulars might play about half the game this week.

"Some guys will play the entire first half, then start the series in the third quarter and others won't be quite that long," Caldwell said without identifying specific players.

Johnson's potential absence would give the Lions more time to assess their group of receivers before cutting down the roster. Johnson and Golden Tate are obviously the top two receivers on the team, but Detroit has several more who will see time Friday.

Greg Salas, who's spent the last three seasons on three different teams' practice squads, is among them.

"There's games to be played still and things to be done," he said. "I just control what I can control and play how I can play and let that speak for itself."

Veterans Lance Moore and Ryan Broyles, along with Jeremy Ross, who returned kicks last season, add experience while the rest of the group in camp is largely untested.

"It's going to be a tight race," Caldwell said. "We need to see some guys separate from the pack.

"Right now there's a pretty good logjam in there where a lot of guys look the same and are performing well. Let's see if someone's got something a little bit different that will separate them from the rest of the guys."

The Lions play their final exhibition game Sept. 3 at home against Buffalo.

Notes: The Lions placed rookie linebacker Kevin Snyder on injured reserve and signed offensive lineman Joe Madsen on Wednesday. . Caldwell said RB Joique Bell, who has been on the physically unable to perform list since the start of camp, will not play Friday against the Jaguars. . DE Ziggy Ansah and LB DeAndre Levy were among the players who did not take part in drills Wednesday.