He had surgery on a torn labrum Tuesday, a source told ESPN NFL Insider Josina Anderson. The source added that Gilmore had the labrum repaired last year on the same side.
"He had it repaired last year and he is one of the best this year at corner, so he will be fine," the source told Anderson. "Hate that (his season) was cut short."
Gilmore started the first 12 games this season and ranks fifth among NFL players with 21 passes defensed, including three interceptions. Pro Football Focus has rated him as the 14th-best cornerback in the NFL so far this season.
Gilmore has been a full-time starter for the Bills since they selected him 10th overall in 2012. The Bills exercised the fifth-year option on Gilmore's contract this past spring, keeping him under contract through next season at a cap number of $11.082 million.
The Bills signed outside linebacker/defensive end Max Valles, a sixth-round pick this season, off the Oakland Raiders' practice squad to fill Gilmore's spot on the 53-man roster.