The Steelers' main injury worry following their 15-6 loss Sunday in Philadelphia was the punishment quarterback Ben Roethlisberger took while being sacked eight times. He played with a slight shoulder separation, and a right hand injury sidelined him late in the fourth quarter.
When Tomlin revealed his updated injury list Tuesday, Roethlisberger wasn't on it, but Parker unexpectedly was -- the Pro Bowl runner has a sprained left knee that will keep him out of Monday night's home game against Baltimore (2-0).
Both the offense and defense will be missing key players. Four-time Pro Bowl defensive lineman Casey Hampton (groin sprain) also won't play and defensive end Brett Keisel (calf) will miss a second successive game. Chris Hoke, who made 10 starts in 2004, replaces Hampton.
Tomlin wouldn't discuss the specifics of Parker's injury or whether he might also miss the Oct. 5 game at Jacksonville, although that seems likely.
With Parker out, first-round draft pick Mendenhall will make his first NFL start. Mendenhall has 28 yards in 10 carries during limited playing time, partly because he fumbled three times in the final two exhibition games.
Is he ready after failing to get any carries in the past two games?
"Ready or not," Tomlin said. "No, Rashard is ready. He's a talented guy. He's been practicing well and he gets his opportunity. You see a lot of his peers around the league and they've been getting opportunities, partly because they don't have Willie Parker playing in front of them."
Matt Forte of Chicago leads NFL rookie rushers with 304 yards and a 101.3 yard average, while Tennessee's Chris Johnson (92.0), Oakland's Darren McFadden (84.0) and Houston's Steve Slaton (79.5) are averaging at least 75 yards per game.
"He gets his opportunity," Tomlin said of Mendenhall. "I'm sure he's excited about it. I know our team is excited to see what he's capable of doing."
Running the ball consistently against the Ravens has been a problem for the Steelers (2-1), even when Parker was healthy.
Parker has averaged 2.6 yards per carry and 43 yards per game in five career starts against the Ravens. With Parker injured, the Steelers managed 46 yards rushing in a regular season-ending 27-21 loss at Baltimore in December
This season, the Ravens have allowed a combined 153 yards rushing while beating Cincinnati and Cleveland.
Parker had 243 yards in his first two games before being held to 20 in Philadelphia, where the running game never got going and Roethlisberger was under persistent pressure. Despite those problems, Tomlin doesn't plan any changes along the offensive line.
Tomlin said everyone shares the blame for the protection breakdowns, including the coaches. The Eagles had nine sacks and held the Steelers to 160 yards, with 33 yards rushing on 19 carries.
"As coaches, we could have done a better job of adjusting and putting those guys in a position to be successful," Tomlin said. "We could have done a better job of identifying on all levels -- wide receivers, running backs, offensive line and quarterback. We could have done a better job of physically blocking them."
No doubt the Ravens saw how effective the Eagles' pressure was, but Tomlin doesn't expect an identical game plan Monday.
This is the second injury in as many seasons for Parker, who was leading the NFL in rushing with 1,316 yards when he broke his right leg early in a Dec. 20 game at St. Louis.
Without Parker, the Steelers were held to 92 yards rushing in their final two games, one reason why they used their first-round pick on Mendenhall.