San Francisco 49ers running back Raheem Mostert will likely miss the rest of the 2018 season after suffering a broken right forearm in the third quarter of Thursday night’s 34-3 win over the Oakland Raiders.With 4:38 remaining in the third quarter, Mostert suffered the injury on a rushing attempt for no gain when he was met with force by Raiders defensive tackle Clinton McDonald. 49ers medical personnel rushed on the field after the play having spotted the gruesome injury from the sideline.Head coach Kyle Shanahan said following the 49ers’ win that San Francisco doesn’t expect to have him for the rest of the season, although trainers did not confirm that to him.”I would assume so with a broken arm,” Shanahan said.Mostert had a 52-yard touchdown run and finished the game with seven carries for 86 yards. He’s averaging 7.7 yards per carry in 2018.