INDIANAPOLIS -- Colts wide receiver Michael Pittman Jr. has been pushing through a painful back injury for weeks. But the injury, at least for this week, has gotten the best of Pittman, who will miss Sunday's game against the Buffalo Bills.

The Colts' No. 1 wideout will miss his first game of the season as Indianapolis (4-5) looks to even its record.

"He's been battling like crazy," coach Shane Steichen said. "We're taking this thing week to week. Like I've said, [he is] one of the toughest guys I've ever been around."

Pittman contemplated a stint on injured reserve last month after the back issue flared up and began significantly impacting him. Pittman said he ultimately decided against IR because he thought he could still help the team in his diminished state.

Earlier this week, Pittman said he has experienced ups and downs while dealing with the injury.

"Some days are really good, and some days you wake up and you're like, 'Oh, here it goes,'" he said.

The loss of Pittman is likely to press rookie Adonai Mitchell into a bigger role for the first time in weeks. Mitchell has averaged 16.4 snaps per game but played just five snaps in Sunday night's loss to the Minnesota Vikings.

"He's improving, so looking forward to him [playing] this week," Steichen said of Mitchell.