OXNARD, Calif. — Dallas Cowboys defensive end Robert Quinn was suspended Thursday for the first two games of the regular season for violating the NFL’s ban on performance enhancers.

Quinn was acquired in a trade with Miami in the offseason. The league said Quinn, a ninth-year player, is eligible to practice and play in preseason games, but is out until the regular season after breaking his left hand in practice at training camp.

Quinn, 29, will be eligible to return in Week 3 at home against the Dolphins.

Quinn’s agent, Sean Kiernan, said in a statement released on Twitter he was “extremely disappointed” in the NFL’s decision to suspend Quinn.

Kiernan said Quinn takes medication to control seizures. The agent said it is believed Quinn’s medication was contaminated with probenecid when a prescription was filled at a pharmacy. Probenecid was used as a masking agent for steroids in the 1980s and ’90s, Kiernan said, but is used now as a prescription drug to treat gout.

49ERS: Quarterbacks C.J. Beathard and Nick Mullens will split time during the preseason opener Saturday against Dallas.

Coach Kyle Shanahan wouldn’t say which one will start.

Shanahan told KNBR Radio in San Francisco that the reps have been even for Beathard and Mullens, who are competing to back up Jimmy Garoppolo. “I wouldn’t say anyone has the edge because I don’t want to go there yet,” Shanahan said.

COLTS: Backup offensive lineman Ian Silberman was transported to a Buffalo-area hospital for precautionary reasons because of what the team called an abdominal medical issue.

The Colts said Silberman was taken to the hospital before the preseason opener against the Bills. The team had no other details on the player’s status.

Silberman has bounced around the NFL since being drafted by San Francisco in the sixth round of the 2015 draft.

RAIDERS: Starting right guard Gabe Jackson went down with a left leg injury that the team fears could be serious during a joint practice with the Los Angeles Rams.

Jackson was injured early in the session when someone rolled into his leg. He was taken off the field on a cart and the owner, Mark Davis, went into the locker room shortly after that for almost 15 minutes.

“We’re concerned, obviously,” Coach Jon Gruden said.

CHIEFS: Kansas City agreed to terms with cornerback Morris Claiborne on a one-year deal to fortify a thin and unproven backfield, a person familiar with the negotiations said.

The person said the deal could be worth about $3 million with incentives.

DOLPHINS: Defensive tackle Robert Nkemdiche signed two weeks after Arizona released its 2016 first-round draft pick.

Nkemdiche is still recovering from ACL surgery last December, and the Dolphins placed him on the active/physically unable to perform list.

BROWNS-TEXANS: Cleveland traded disgruntled running back Duke Johnson to Houston for an undisclosed 2020 draft pick.

Johnson has been unhappy with his role in past seasons. He asked to be traded this year after the Browns signed suspended free-agent running back Kareem Hunt.