It’s dangerous to be a 49ers safety.
With starters Jimmie Ward and Eric Reid already sidelined with leg injuries, Jaquiski Tartt, who is No. 3 on the depth chart, left practice Monday walking gingerly and favoring his left side after breaking up a pass.
Head coach Kyle Shanahan said the issue was “ribs-type stuff” and acknowledged the 49ers might need to sign a safety to help them get through training camp.
On Monday, they finished practice with Vinnie Sunseri and undrafted rookie Lorenzo Jerome on the first team. Their other safeties are undrafted rookie Chanceller James and Don Jones. Cornerbacks Will Davis and rookie Adrian Colbert also have experience at the position.
Shanahan has said Ward (hamstring) could be sidelined until mid-August. Reid (ankle) figures to return sooner. A day after leaving practice early, Reid was walking without a limp Monday.
Reuben redux: It turns out Nick Mullens vs. Reuben Foster isn’t a fair fight.
For the second straight day, Mullens, an undrafted rookie, threw a short pass that was picked off by Foster, the No. 31 pick.
It was Foster’s third interception in four training-camp practices, but Shanahan explained why it might have been his personal favorite. Foster’s interception Monday came on the same play that fooled him the previous day.
On Sunday, Foster responded to the play by defending the run, which allowed a wide receiver to run wide open in the area he vacated. Shanahan’s point: The rookie quickly learned from his mistake.
“He had the same play today and he didn’t fill up in the run, and he dropped back and got a pick,” Shanahan said. “It’s one play he got beat on bad yesterday and today we ran the same play at him and he got an interception off it. So that’s what you want to see.”
Roster move: The 49ers claimed undrafted rookie wide receiver Tim Patrick off waivers from the Ravens and waived undrafted rookie wideout BJ Johnson, who sustained a hamstring injury Friday.
Patrick led Utah in receptions (61), yards (888) and receiving touchdowns (5) last year.
Injury report: Rookie tight end George Kittle (hamstring) and cornerback Keith Reaser (knee) did not practice and are listed as day-to-day. Undrafted rookie center JP Flynn (knee) missed his second straight practice.
Eric Branch is a San Francisco Chronicle staff writer. Email: EBranch@sfchronicle.com Twitter: @Eric_Branch