Coach Kevin Stefanski described Njoku's status as week-to-week when he addressed the media Monday.
The Browns (2-5) next play the Cincinnati Bengals on "Monday Night Football" (Oct. 31) before a bye week.
Browns starting linebacker Jacob Phillips, meanwhile, likely will miss the rest of the season with a pectoral injury. Phillips had taken over signal-calling duties after captain Anthony Walker Jr. suffered a season-ending quadriceps injury in Week 3. Stefanski said Phillips got hurt while making a tackle near the sideline.
Medical tests revealed that Phillips has a torn pectoral and likely will need surgery that would end his season, a source told Schefter.
Also Monday, Stefanski said top cornerback Denzel Ward remains in concussion protocol. He's missed Cleveland's past two games after getting hurt in the fourth quarter against the Los Angeles Chargers on Oct. 9.
Njoku suffered the injury in the second half of Cleveland's 23-20 loss Sunday to the Baltimore Ravens. He went to the locker room during the third quarter and didn't return, eventually leaving the stadium in a walking boot and on crutches.
Later Sunday, Njoku tweeted: "Be back soon."
Njoku was leading the Browns with seven catches on seven targets for 71 yards before leaving the Baltimore game. On the season, he has a team-high 34 receptions for 418 yards and a touchdown.
The Associated Press contributed to this report.