Pryor, who made 77 catches for 1,007 yards and four touchdowns for the Browns last season, has lost his starting job to Josh Doctson. He has only 20 receptions for 240 yards and a touchdown through eight games.
Still, Washington declined to deal him.
Cleveland would have gotten Pryor for $1.5 million for the second half of the season. He signed a one-year deal with Washington with $6 million guaranteed.
He would have joined a wide receiving corps in Cleveland that soon will see the return of Corey Coleman and Josh Gordon. Coleman has a hand injury and could return from injured reserve next week; the league has conditionally reinstated Gordon, with his return to the field expected in Week 13.