Chris Kuper appeared to know something was wrong as soon as he climbed off the ground in a team drill early in Tuesday’s practice.

Kuper, a veteran right guard and the team’s best all-around blocker, went straight to a Broncos’ athletic trainer and quickly headed to the locker room, where X-rays revealed he had broken his ulna, one of the bones in his left forearm.

The injury is expected to sideline Kuper for six weeks, which will likely include the remainder of the preseason and the Broncos’ first three regular-season games.

Backup interior lineman Manny Ramirez replaced Kuper for the rest of Tuesday’s practice, and is expected to remain there for the foreseeable future.

“You’re concerned about all of them, because you want them out there. This is how you get better,” coach John Fox said after Tuesday’s practice, addressing a question about the team’s expanding injury list. “We take a next-man-up approach, and it gives the man behind them an opportunity.”

Five other players did not participate in the practice, and two others, in addition to Kuper, left the workout early with injuries. But only Kuper’s injury appears serious enough to stretch into the season. The other players missing all or part or the session because of physical issues were linebackers Keith Brooking (hamstring) and Danny Trevathan (ankle), safety Quinton Carter (knee/hamstring), cornerback Tracy Porter (illness), wide receiver Tyler Grisham (knee), defensive end Jason Hunter (triceps) and running back Ronnie Hillman (hamstring).

This is Kuper’s second significant injury this calendar year. In the final game of the 2011 regular season, on Jan. 1, Kuper suffered a gruesome injury to his lower left leg and ankle. Kuper tore multiple ligaments and broke his fibula when his ankle was dislocated.

Kuper had multiple surgeries to repair that injury, and he was just cleared to return to practice when training camp began in late July. The team was easing him back into full-time action, including leaving him on the sideline in last week’s preseason opener as a precaution.

His new injury came during a routine play during an 11-on-11 drill in practice.

Kuper, a fifth-round pick in 2006, has been a full-time starter since midway through the 2007 season. He signed a contract extension, which included about $13 million guaranteed, in 2010 and is the team’s highest-paid offensive lineman. He also has been a team captain.

Ramirez has played in 20 games in five seasons in the NFL, including two games for the Broncos last season. He filled in for Kuper at right guard throughout offseason workouts and the minicamp.

The Broncos also have experimented in camp with moving right tackle Orlando Franklin to guard, though that move would require the team to promote one of the backup tackles, either Chris Clark or Ryan Harris. Franklin, a second-round pick in 2011, played three snaps at guard with the second-team offense in last week’s preseason game at Chicago.

Lindsay H. Jones: 303-954-1262, ljones@denverpost.com or twitter.com/lindsay_h_jones