The 2-2 Raiders are now in third place in the loaded AFC West division while Carr, needless to say, can't come back soon enough.
After both opened the season with two wins that boosted confidence and expectations, the Ravens (2-2) and Raiders (2-2) come into Sunday's meeting in Oakland on two-game losing streaks with a growing number of doubters.
With the running game stalled, the Raiders' entire offense has struggled.
But strong safety Eric Weddle did agree that there is a drop-off between Carr, who threw 28 touchdown passes and only six interceptions last season, and Manuel, whose best season is an 11-touchdown, nine-interception showing in 2013.
If Carr's injury lingers, Manuel could even get a chance to start the Raiders' Week 8 game against the Buffalo Bills at New Era Field. He just really enjoys coming to work and putting in a hard day's work. If he was, he'd be starting somewhere. We only had one sack last week, and we have to get that total at least doubled.
At 6 feet 4 and 237 pounds, Manuel is slightly bigger than the 6-3, 215-pound Carr and has rushed for 324 yards and four touchdowns.
"Marshawn Lynch is one of the best running backs in the league", Harbaugh said.
"It certainly helps you get to more of your plays", offensive coordinator Todd Downing said. "But he's definitely going to run the same offense". It raises the importance of every game and the New England Patriots showed on Thursday night that they aren't going away either. And you could see in the Denver game and in the preseason, he runs the offense well. "We're close. That's the thing that makes it so frustrating". It will be just his fourth start since the beginning of the 2015 season.