49ers rookie LB Foster limited by injury to right shoulder

San Francisco 49ers' Reuben Foster signals during a joint NFL football practice with the Denver Broncos. (Marcio Jose Sanchez/AP Photo)

SANTA CLARA, Calif. — San Francisco 49ers rookie linebacker Reuben Foster has a mild AC joint sprain in his surgically repaired right shoulder.

Foster was held out of contact during practice Thursday with the Denver Broncos because of the injury. The team says the injury is not related to the torn rotator cuff that Foster had an operation on before the draft.

That injury helped contribute to Foster sliding in the first round before San Francisco traded up to No. 31 to draft the former Alabama linebacker. Foster has been impressive so far in camp and has moved into a first-team role at linebacker.

Coach Kyle Shanahan said he expects Foster to be able to play in Saturday’s exhibition game against Denver.

"He actually was very upset with me that he didn’t (practice)," Shanahan said. "We were just being safe with him. We know he hasn’t been on it very long. It was sore after yesterday. It’s something that happens, especially with linebackers a lot."

Foster participated in individual and seven-on-seven drills in practice Thursday and also got involved in a minor fight after teammate Pita Taumoepenu got knocked over by a Denver offensive lineman.

That was one of three skirmishes on the day, following a mostly peaceful first day of practice between the teams.

"We didn’t want that but we got past that and practiced," Denver coach Vance Joseph said. "Both sides were being really competitive. It’s football. It’s a physical sport. Some of that stuff is going to happen but then both sides got their composure."

All three fights happened early in practice, including one that started when San Francisco receiver Pierre Garcon took exception to being blocked by Aqib Talib following an interception.

"Aqib just made a regular block like we do in interception drills and Garcon just tackled him," Denver cornerback Chris Harris Jr. said. "It was definitely dirty. He and Aqib squashed it out. I guess everything is good."

The 49ers are thin at linebacker right now after losing potential starter Malcolm Smith to a season-ending torn pectoral earlier in camp. The team placed Donavin Newsom on injured reserve and waived Jayson Dimanche with an injured designation earlier this week.

Starter NaVorro Bowman also left practice early with a stinger Thursday that is not expected to be serious.

The 49ers signed linebacker Shayne Skov to a one-year deal for more depth at the position. Skov spent the past three seasons with San Francisco, appearing in 24 games. He was waived in May.