The highly regarded rookie was not in pads, his left leg was wrapped, and he did not participate in practice at all on Tuesday.
"There's a chance he won't play on Friday," coach Pat Shurmur said. "He's got a sore knee and is being evaluated."
It could be the result of going full-bore the past two weeks on a knee that was surgically repaired this spring. That's one of the reasons Richardson did not fully participate in the NFL combine in April.
"It was a little scope," Richardson said at the time of what was termed minor surgery. "I don't even call it a setback."
It didn't keep Cleveland from trading up to No. 3 in the draft to select the tailback who helped lead Alabama to the national championship. And it didn't prevent the Browns from signing Richardson to a four-year, $20.5 million contract.
"I'm always concerned about injuries," Shurmur said. "He's been practicing well. We'll just have to see where he is."
Richardson has been quite impressive in camp, displaying quickness and toughness. He did miss practice time last week with what Shurmur said was a headache.
Richardson, starting tight end Ben Watson and a few others limited by various ailments rode stationary bicycles as the team went through regular drills on Tuesday.
Shurmur didn't seem as worried about Watson, who missed time last season with a concussion. He stopped short of saying the nine-year pro would play when Cleveland opens the preseason Friday in Detroit.
"He's doing fine," Shurmur said. "He'll be back out here soon. We're dealing with some soft tissue (issues)."
Shurmur also said Marcus Benard was "doing fine," though the linebacker was nowhere to be seen during drills after walking off midway through practice on Monday.
Cleveland will face the Lions without at least two starters on defense. Linebacker Chris Gocong is out for the season with a torn right Achilles tendon. Lineman Phillip Taylor, last year's No. 1 pick, will be sidelined until at least mid-October after a torn pectoral muscle repaired this spring.
If Richardson can't play, Montario Hardesty will get the chance to show if he has progressed. A second-round choice from Tennessee in 2010, he tore up his left knee in the preseason that year and missed the entire season. In sporadic time a year ago, he rushed for 266 yards in 10 games.
Hardesty, in better shape now after dropping about 10 pounds down to 215, is eager to play.
"Now I can play without being hurt and thinking about it," he said. "This might be the best I've ever felt. I feel like I've really got a lot to prove. I've got a chip on my shoulder, and I've just got to go out and play every day."
That's fine with Shurmur.
"I want to see efficient play," Shurmur said of Hardesty and former Green Bay running back Brandon Jackson, who also will log time against the Lions. "I want to see strong running and catching the ball. When we throw the ball, I want to see pass protection."
Practice was delayed 30 minutes, as team executives were a tad late returning from Philadelphia, where they attended a memorial service for Garrett Reid, son of Eagles coach Andy Reid. ... WR Josh Gordon dropped a pinpoint pass from new starting QB Brandon Weeden over the middle. Shurmur said the rookie, who didn't play at all last season at Utah, is among players pushing through normal midcamp fatigue. ... P Reggie Hodges, holder on placekicks, passed to OT Joe Thomas in the end zone on a fake field goal. It fell incomplete. ... Rookie John Hughes and third-year pro Scott Paxson are splitting time at Taylor's defensive line spot. ... Rookie DB Trevin Wade picked off a wayward pass by QB Colt McCoy, now battling Seneca Wallace for the backup spot. ... The Browns will practice in front of fans Wednesday night at their own downtown stadium, going through red zone and special teams drills in addition to what Shurmur called "moving the ball."