Riether was not punished for his actions by referee Lee Probert, which came in the last minute of Fulham's 3-1 defeat at Craven Cottage.
"For me it was a red card for the right-back," the Belgian told MUTV. "I hope the referee looks at the video later."
United manager David Moyes was more philosophical after his team extended their unbeaten run.
"We are never going to ask for (protection)," said Moyes.
"We want (Januzaj) to get up. We don't want him to go down easily.
"He is a really honest boy and I thought there were a couple of times when fouls should have been given against him but they weren't."