Pittsburgh Steelers doctors are hopeful, though hardly optimistic, that quarterback Ben Roethlisberger will be able to return from his rib and shoulder injuries Dec. 2 against the Baltimore Ravens, according to a source familiar with the situation.

Steelers doctors believe Roethlisberger will miss three weeks, though the team has not abandoned hope that he may miss only two games and be able to return for the rematch against the Ravens.

Roethlisberger was ruled out of Sunday night's game against the Ravens and is not expected to play next Sunday at Cleveland.

Though Roethlisberger said the injury to his first rib on his right side threatened his aorta, a source said doctors believe the greater threat is to the surrounding arteries, vessels and soft tissue.

Roethlisberger was in as much pain Friday as he was Monday, a source said, and the timetable for his return is somewhat unpredictable. The injury is rare and needs to heal itself -- there's no treatment or procedure that can fix it quicker.

While Roethlisberger missed Sunday night's 13-10 loss to the Ravens, running back Rashard Mendenhall started and rushed 11 times for 33 yards.

And safety Ryan Clark, who has suffered two concussions in the last three weeks, told ESPN that he would wear a special helmet which is one size bigger than usual and packed with bullet-proof Kevlar against the Ravens.

ESPN's Rachel Nichols contributed to this report.