On a conference call with Bay Area media on Monday, Niners coach Kyle Shanahan said an MRI revealed that Coleman had the injury. Shanahan also ruled Coleman out for this week's game against the Cincinnati Bengals with the expectation that it would be a bit before Coleman can return.
"[I'm] pretty sure he's not going to be around this week and we'll take it week to week after that," Shanahan said.
Asked if it was possible that Coleman could land on injured reserve with the potential to return after eight weeks, Shanahan indicated the recovery probably wouldn't take that long.
"I don't think IR is a possibility right now so I think we'll ride it out," Shanahan said.
According to Shanahan, Coleman was injured on the 49ers' first offensive play against the Bucs. Coleman attempted to play through the ailment but the additional snaps apparently only made it more difficult.
"I think he landed on his ankle and then it just got worse as the game went," Shanahan said. "He tried to battle through it throughout the second quarter."
The Niners removed Coleman from the game at halftime and he did not return after posting 23 yards on six carries and 33 yards on two receptions. After the game, Shanahan acknowledged he was concerned about Coleman's status with the running back set to have further tests done on the ankle Monday morning in Youngstown, Ohio, where the Niners are spending the week leading up to Week 2.
With Coleman expected to miss some time, the Niners will turn to a combination of Matt Breida and Raheem Mostert to fill the void. That duo stepped in for Coleman on Sunday with limited success, combining for 25 touches and 77 yards, though they had some important first downs in the second half.
Breida appears to be the favorite to handle the starting job after running for 814 yards last season despite being limited by recurring ankle injuries. Mostert is San Francisco's best special teams player but also flashed potential in 2018 when he averaged 7.7 yards per carry on 34 attempts before his season ended with a broken arm. Both figure to get plenty of opportunities in Coleman's absence.
As for a temporary replacement on the roster, Shanahan said that decision won't be made until later this week. The obvious candidate is practice squad back Jeff Wilson Jr., who played in six games with two starts and averaged 4 yards per carry last year for the Niners.
Whether Wilson gets the promotion will depend on how healthy the rest of the team is as it heads into Sunday.
"We have got to see how the week goes, how many we're going to need on Sunday," Shanahan said. "There's plenty of time. In Atlanta [where Shanahan served as offensive coordinator], I think we played every game but like two or three with only two running backs, so sometimes that's a risk you take in a game. It all just depends on how the rest of our roster is and what we feel gives us the best chance by Saturday."