Just when Broncos RG Chris Kuper had worked his way back from a fractured fibula and torn ankle ligaments, another injury struck that will sideline him into the regular season.

Kuper injured his left forearm during practice Tuesday morning. The Denver Post reported that the injury is a fracture, and will sideline him for the next six weeks.

Manuel Ramirez will step in for Kuper. He was the first-team right guard throughout the offseason, which Kuper missed because of his leg and ankle injuries, and played there with the first team in the preseason opener last Thursday at Chicago, since Kuper was not yet back to full speed.

Ramirez was inactive for 14 of 16 regular-season games last season and hasn't started a game since 2009, when he was the Detroit Lions' left guard for a dozen games.

Kuper's injuries are easily the most significant to strike the offensive line the last two years. He is the only member of the Broncos' first-team quintet to miss any starts to injuries since they were first placed together at the start of last season.

For up-to-the-minute Broncos updates, follow Andrew Mason on Twitter at @CBSSportsNFLDEN and @MaxBroncos.