The Patriots placed Montgomery on injured reserve Tuesday due to an apparent aggravation of a right knee injury, Mike Reiss of ESPN.com reports.
After initially injuring his knee Aug. 26 and turning in only limited participation in practice last week, Montgomery was listed as questionable ahead of Sunday's game against the Dolphins. He ultimately gained clearance to play in the Patriots' season-opening 20-7 loss, logging 21 snaps while accounting for 13 yards and New England's only touchdown across five touches (two carries, three receptions). With Montgomery's move to IR ensuring that he'll miss at least the next four games, rookie Pierre Strong or practice-squad running back J.J. Taylor could step in as the third option in a backfield rotation headlined by Damien Harris and Rhamondre Stevenson.