The 30-year-old was involved in an indicent during United’s 3-1 win over Fulham at Craven Cottage on Saturday.
Riether and team-mate Pajtim Kasami tangled with Januzaj as the United winger tried to run down time.
“That would be disappointing,” Fulham boss Martin Jol said about a potential ban. “If it is true, then we have to talk to him.
“I have got some good back-up players as well, so that is not a disaster. The result is a disaster.”