(Reuters) - Quarterback Ben Roethlisberger is out of the Pittsburgh Steeler's divisional clash with the Baltimore Ravens on Sunday and could be out even longer with a worrying rib injury.
Veteran back-up Byron Leftwich will make his first start for the Steelers, replacing the two-time Super Bowl winner Roethlisberger.
Roethlisberger sprained a joint in his right shoulder against the Kansas City Chiefs on Monday when he was sacked by linebacker Justin Houston in the third quarter.
But on Wednesday he highlighted another more serious injury, to his first rib, which could keep him sidelined much longer.
"That's the more scary part because I guess if it goes in the wrong direction it could puncture the aorta," Roethlisberger told reporters on Wednesday in comments reported by the Pittsburgh Post-Gazzette.
Roethlisberger said he will have to let the rib injury heal but did not believe his season was over.
"I'm going to get back as soon as I can, I know that much," said the quarterback, who added he had spent the last two nights trying to sleep in a chair.
Leftwich came in for Roethlisberger, going 7-for-14 for 73 yards in his first regular season game in almost two years.
The Steelers won 16-13 after an over-time field goal.
The 32-year-old Leftwich was drafted by the Jacksonville Jaguars with the seventh pick of the first round of the 2003 draft but was cut in 2007 and has mainly been a back-up since with Atlanta and Tampa Bay, as well as an earlier spell at Pittsburgh.
While Leftwich is an experienced back-up, the loss of Roethlisberger is a major blow for the Steelers (6-3) who trail the Ravens (7-2) in the AFC North.
After facing the Ravens at home, Pittsburgh have another divisional game at the Cleveland Browns before traveling to Baltimore for the return game on December 2.
(Reporting By Simon Evans, editing by Julian Linden)