San Francisco 49ers cornerback Richard Sherman is reportedly headed to injured reserve.

NFL Network’s Ian Rapoport said Wednesday that the All-Pro veteran is nursing a calf strain, with rest and rehabilitation being the best medicine.

The 49ers hadn’t announced any news on Sherman as of early Wednesday afternoon, although a trip to the IR will sideline him for at least three weeks.

His backup, Ahkello Witherspoon, is in the concussion protocol, according to The Athletic. Witherspoon played four snaps on defense and 13 on special teams in the 49ers’ 24-20 season-opening loss to the Arizona Cardinals, logging one tackle.

Sherman did not appear to be hampered by an injury on Sunday and played 78 of 82 defensive snaps. The 32-year-old allowed just one catch on two targets for 9 yards in the loss, per Pro Football Focus.

Sherman recorded 61 tackles, three interceptions and 11 passes defensed in 15 games last season while making his fifth Pro Bowl.

Sherman’s first seven seasons were spent with the rival Seattle Seahawks, with whom he earned four Pro Bowl selections, made two Super Bowl appearances (winning one) and grabbed 32 interceptions.

The 49ers are also signing former Pittsburgh Steelers CB Brian Allen to the practice squad, according to his agent. Allen has played in 16 career games.