The injury is believed to have happened in the first half, according to head coach Leslie Frazier. Robinson played 28 of the 52 defensive snaps.
The second-year cornerback moved into a starting role this year, taking over for Antoine Winfield after the Vikings elected to release the long-time veteran. Robinson struggled early in the season but had played better of late, credited with 52 tackles, including five for a loss, three quarterback hurries, seven passes defensed and one forced fumble this year.
"It had been bothering him for a little while and at some point he ended up making a tackle and he couldn't get the wind back that he needed to be able to go out and run," Frazier said. "We talked to him on the sideline, I think it was beginning of the second half … we noticed it in the first half, we come out the second half, talked to him a little bit and decided not to let him continue until we got a look at it and found out today he suffered a fracture."
Frazier said it might be possible for Robinson to return yet this season, but with the injury expected to take four to six weeks to heal, the more likely option is that Robinson will be placed on season-ending injured reserve in the coming days.
For the season, Robinson had played in 80.5 percent of the defensive snaps.
Rookie Xavier Rhodes is expected to replace Robinson in the base defense and Marcus Sherels in the nickel defense.
Frazier said RB Adrian Peterson's groin injury will be a concern this week.
"We're still getting some medical information," Frazier said. "My understanding is he should be ready to go, but I still need to get some other information."
Center John Sullivan suffered a concussion and will have to pass the NFL-mandated post-concussion protocol before he plays again.
Joe Berger, who replaced Charlie Johnson at left guard for the Redskins game, played the final 21 snaps for Sullivan at center on Sunday.
The Vikings will also monitor the status of receiver Greg Jennings and his Achilles tendon. Jennings was listed as probable on Friday's injury report but was a surprise deactivation Sunday.
"There was nothing in my mind that made me think on Friday that he wouldn't be able to go," Frazier said. "It wasn't until maybe Saturday night when I talked to him right before our team meeting that I got a hint that there was a potential chance that he might not be able to go, and even then I thought he'd be fine when he got up the next day to work out and see how he'd be. Just wasn't able to do it so we had to scratch him. That was a tough one because we did expect him to be able to play."
Tim Yotter is the publisher of Viking Update. Follow Viking Update on Twitter and discuss this topic on our message boards. To become a subscriber to the Viking Update web site or magazine, click here.