The tumultuous season of Indianapolis Colts All-Pro linebacker Shaquille Leonard is taking another detour.

After he was ruled out of the Sunday game against the Las Vegas Raiders earlier Friday, the Colts now are planning to place Leonard on injured reserve after a setback in his road to returning from offseason back surgery, sources told ESPN's Adam Schefter.

The decision means Leonard will miss at least four of the Colts' eight remaining games.

Interim head coach Jeff Saturday said Friday that Leonard did not finish the Wednesday workout because something "felt different" with the back and nerve-related issues Leonard has been dealing with since undergoing surgery in June.

"They scanned him and they're working with him, evaluating him," Saturday said of the team's medical staff.

Leonard has played in just three games this season. He made his debut in Week 4 on Oct. 2 but sustained a broken nose and concussion in that game after a collision that bent his face mask. Leonard returned to action in Week 8 but now will be sidelined again after playing in the Colts' past two games.

It has been a frustrating several months for Leonard, who doctors discovered had an impinged nerve in his back, causing lower body pain. Leonard expanded on the slow progress earlier this week.

"Each week I've felt better, starting from my first week of practice, not being able to move and being stiff," he said. "In the past two games, I see myself moving around better. But we're still not there. The nerve still isn't firing in my calf."