HUGE loss for them. Crabtree became a legit top 10-15 WR last year, 85 receptions 1,105 yards and 9 TDs. If he's done for the year, that puts the 49ers from the 1/2 best team in the league to the texans/packers area around 6/7, giving the Seahawks the clear edge IMO in the West.
Veteran Boldin is clutch, but not a #1 WR at this point. Manningham is an average #2 WR/nothing special. Both can be contained 1 on 1 with good corners.
Remove Crabtree from the pats game (7 receptions 107 yards 2 TDs), and they don't put up 41 on us.