Not much went wrong for the 49ers -- look away Robbie Gould -- in their 31-3 blowout win over the Browns at Levi's Stadium on Monday night. San Francisco's offense was firing on all cylinders, its defense was relentless and at least Gould didn't miss all four of his field-goal attempts. 

Not everything is perfect, however, even when you're undefeated for the first time since 1990. The 49ers will be without fullback Kyle Juszczyk for four to six weeks after spraining his MCL in the win, the team announced Tuesday. 

Juszczyk injured his knee while blocking for running back Matt Breida in the third quarter against the Browns. The do-it-all fullback immediately grabbed his left knee and remained on the turf. Juszczyk was taken into the medical blue tent, and soon thereafter, went to the locker room on a cart.

Head coach Kyle Shanahan announced after the win it was believed Juszczyk sprained his knee. An MRI Tuesday confirmed that fact.

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While fullback might be a lost position in the modern NFL, Juszczyk is in a league of his own. The 28-year-old has been named to the Pro Bowl the last three seasons -- once with the Ravens, twice for the 49ers -- and truly is a triple threat. He can serve as a blocker, ball carrier or receiver. 

Juszczyk has 6 yards rushing and 76 yards receiving this season while constantly creating open holes for his running back. There's no doubt he will be a major loss for the 49ers' run-dominant offense.