PITTSBURGH -- Steelers running back Chris Fuamatu-Ma'afala will miss at least two games with a torn pectoral muscle that will not require surgery.

The injury leaves the Steelers thin at what usually is their deepest position. Jerome Bettis (knee sprain) sat out a 31-18 victory Sunday at Baltimore and is listed as doubtful for Sunday's game at Cleveland.

Fuamatu-Ma'afala was hurt on the Steelers' final possession when a Ravens defender tried to pull the ball from his hands.

Even with the injuries, coach Bill Cowher said he is comfortable with Amos Zereoue and rookie Verron Haynes at running back and doesn't anticipate any roster moves.

Haynes will spend the week practicing at tailback rather than at fullback, where tight end Matt Cushing will be Dan Kreider's backup.

With Bettis out, Zereoue carried 13 times for 53 yards and two touchdowns and Fuamatu-Ma'afala gained 21 yards on eight carries in Baltimore. Haynes ran three times for 23 yards, his first carries in the NFL.