Njoku went to the locker room in the third quarter and was ruled out from returning.
He was in a walking boot and on crutches after the game, but a source told ESPN's Adam Schefter that Njoku suffered a sprained ankle that "isn't serious." He will undergo additional tests to determine the full extent of injury but "he will be OK," the source said.
Njoku tweeted: "Be back soon."
He was leading the Browns with seven catches on seven targets for 71 yards before leaving the game.
For the season, Njoku now has 34 receptions for 418 yards and a touchdown.