Detroit Lions running back Ameer Abdullah has a torn ligament in his left foot, and the team believes he will miss the rest of the season, a source told ESPN's Adam Schefter.

The Lions placed Abdullah on injured reserve on Wednesday but did not disclose how long he will be sidelined.

Due to a change in NFL rules for this season, each team can designate one player placed on injured reserve to return later in the season. Players designated to return are allowed to return to practice in six weeks, but must miss a minimum of eight games. In previous seasons, teams had to designate that a player would return when they submitted the IR move.

Abdullah injured the foot during the second quarter of last Sunday's 16-15 loss to the Tennessee Titans on a 24-yard run in which he broke multiple tackles. At the end of the run, he hobbled off the field and went almost directly into the team's locker room. He did not return.

Lions RB Ameer Abdullah rushed for 101 yards on 18 carries before going on IR with a foot injury. Scott W. Grau/Icon Sportswire

Initial X-rays on the foot showed no broken bones, a source said, but Abdullah went to Charlotte on Tuesday for a second opinion with specialist Dr. Robert Anderson.

Abdullah was Detroit's No. 1 running back, gaining 101 yards on 18 carries this season. He also caught 5 passes for 57 yards and 1 touchdown.

With Abdullah out, Theo Riddick becomes Detroit's top running back, with rookie Dwayne Washington and second-year pro Zach Zenner also having roles. The Lions worked out one of their former running backs, Joique Bell, on Tuesday, according to ESPN Insider Adam Caplan, but Bell has not signed with the club.

ESPN Lions reporter Michael Rothstein contributed to this report.