"It is in David's best interest to find a new team at this time," agent Drew Rosenhaus said, per Schefter.
Njoku appeared in just four games last season with one start, finishing the year with five catches for 41 yards and a touchdown.
A Week 2 wrist injury forced the tight end to injured reserve and he only caught one pass upon coming back in Week 14.
It was a disappointing campaign for the 2017 first-round pick, who appeared ready to break out after totaling 56 catches for 639 yards and four touchdowns the previous season.
New offensive coordinator Alex Van Pelt admitted Njoku was in the "dog house" with the last staff, but he will get a fresh start under new coach Kevin Stefanski, via Anthony Poisal of the team's official site.
"To have him with the ability he has both athletically to play in line or get him out in space and get some matchup issues with safeties and linebackers covering him, I am excited to see what he has to offer," Van Pelt said of the tight end.
His upside is also part of the reason the Browns picked up his fifth-year option for 2021 worth $6 million, per Spotrac.
"We still have a ton of belief in David and he is very talented," general manager Andrew Berry said in April. "Obviously, he was not on the field much last year but he is a guy with outstanding physical tools, he has proven NFL production and we still think the future is very bright with him here."
It's clear Cleveland still has faith in the 23-year-old, but Njoku and his agent are seeking a new opportunity elsewhere around the NFL.