LOS ANGELES -- Los Angeles Rams coach Sean McVay didn't give a specific timeline for injuries to running backs Kyren Williams and Ronnie Rivers, but said "the initial prognosis looks like it's going to be challenging for those guys in the immediate future."
An MRI on Monday revealed Williams has a sprained ankle that is expected to sideline him for Sunday's game against the Steelers but is not considered a long-term injury, a source told ESPN's Adam Schefter earlier in the day.
"Those guys are going to be out for a little bit," McVay said. "Exactly how long we're kind of working through, but that's tough information for both those guys who've done a really good job."
Williams sustained the injury in Sunday's 26-9 victory over the Cardinals, a game in which he rushed for a career-high 158 yards and a touchdown.
He got 154 of those yards in the second half, becoming the first Rams player since Marshall Faulk in 2001 to have at least 150 rushing yards in a half, according to ESPN Stats & Information.
Williams' backup, Rivers, injured a knee early in the second half Sunday. If he can't play against the Steelers, rookie sixth-round pick Zach Evans will likely get the start at running back. McVay said the Rams are still "working through" the plan without Williams and Rivers, however.
"Obviously you saw Zach Evans get the first carries," McVay said. "We've got Royce Freeman on our practice squad, and there'll be some different things that we're in the midst of working through right now.
"And so we'll probably have a little bit better idea once you get the full gauntlet of what it exactly is looking like projection-wise on both Ronnie and Kyren, how that will affect any sort of decisions as it relates to the roster and then what it looks like for the landscape of the league."
Through six games this season, Williams has 456 rushing yards on 97 carries and 105 receiving yards on 13 catches.
The second-year player came into the season as the Rams' No. 2 back but, after the opener, earned the No. 1 spot. Cam Akers, who began the season as the starter, was inactive in Week 2 and then traded to the Vikings, leaving Williams as the clear lead back.
Williams has seven total touchdowns this season (six rushing, one receiving).