Kuper got caught at the bottom of a pile during team drills
early in practice and retreated to the team's Dove Valley
headquarters for X-rays.
The Broncos expect the seven-year veteran to fully recover within four to six weeks.
If Kuper is sidelined for the full six weeks, he would miss the Broncos' first three regular-season games. Denver opens its season against the Pittsburgh Steelers on Sept. 9.
The stalwart of an otherwise young offensive line, Kuper was
making progress in his return from a serious injury to his left leg. He started all 16 games last season but suffered fractures to his ankle and fibula in the regular-season finale.
The Broncos have listed veteran guard Manny Ramirez as Kuper's primary backup on their official depth chart.
"You're concerned about all of (the injured players)," Broncos coach John Fox told the team's website. "You'd like them out there because this is how we get better. But we take a next-man-up approach, and it gives the guys behind them an opportunity."
Information from The Associated Press was used in this report.