Source - Rams RB Kyren Williams (ankle) likely out vs. Steelers - ESPN

An MRI on Monday revealed that Rams running back Kyren 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.

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 rushed for 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 research.

Through six games this season, Williams has 456 rushing yards on 97 carries and 105 receiving yards on 13 catches.

The second year running back came into the season as the Rams' No. 2 back but, after the season 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 in Los Angeles.

Williams has seven total touchdowns this season (six rushing, one receiving).

Williams' backup, Ronnie Rivers, injured his knee early in the second half of Sunday's game. If he can't play against the Steelers, rookie sixth-round pick Zach Evans would likely get the start at running back.

ESPN's Sarah Barshop contributed to this report.