Howard suffered ankle and foot injuries when he was tackled from behind in the second half of Sunday's loss to the New York Giants. On the play, Howard's ankle bent sideways.
He was able to leave the field under his own power but did not return.
A source said the ankle injury will not require surgery.
Howard, the Bucs' first-round draft pick in 2017, finishes the season with 34 catches for 565 yards. His five touchdowns are tied with wide receiver Mike Evans for the team lead.
The Tampa Bay Times first reported news of the IR designation.