CLEVELAND -- The Steelers took another body blow of an injury when they lost starting halfback Rashard Mendenhall with a possible ACL tear in his right knee and they might lose safety Ryan Clark to the potential hazards to him playing in the high altitude in Denver.

Mendenhall went down late in the first quarter without being hit, and coach Mike Tomlin said he feared it was an ACL tear, which requires a 6- to 8-month rehabilitation.

Whatever it is, he will not play in Denver and likely is out for the playoffs.

"It's not good, of course, when a guy goes down in open grass not touched by anyone," Tomlin said. "Experience tells me that, generally, that's not good."

Isaac Redman , who rushed for 92 yards against the Browns, and rookie John Clay , on the practice squad two weeks ago, are the team's only healthy running backs. Veteran Mewelde Moore , who missed the past two games with a MCL sprain in his knee, could return for the playoff game in Denver.

Quarterback Ben Roethlisberger criticized Cleveland fans for their reaction when Mendenhall was hurt.

"I know these Browns fans are passionate about their Browns but when you hear fans cheer when a guy goes down, that's really disappointing," he said.

Clark did not play the most recent time the Steelers were in Denver in 2009, because of the violent reaction his body had when they played there in '07. He has the sickle cell trait and the exertion of playing in Denver prompted a reaction by his blood that caused him to lose his spleen and gall bladder, ended his season and nearly his life.

Tomlin, Clark and others will discuss the situation today and perhaps decide by Tuesday if he will play. Clark said he will follow the advice of the doctors and his coach.