Veteran defensive back Captain Munnerlyn, who played for Sean McDermott with the Carolina Panthers, was signed by the Bills on Saturday, the team announced.
Munnerlyn, 31, spent the last two seasons with the Panthers in his second stint with the team. He played five years with Carolina and then spent three years with the Minnesota Vikings before rejoining the Panthers before the 2017 season. He was released in February.
Munnerlyn has played in 154 career games with 12 interceptions, six forced fumbles and 522 tackles.
He was drafted by the Panthers in the seventh round in 2009 when current Bills GM Brandon Beane was the Panthers' director of football operations and re-signed with the Panthers in February 2017 when Beane was the assistant general manager.
According to NFL Network's Ian Rapoport, the Bills worked out Munnerlyn and cornerback Coty Sensabaugh on Saturday, opting to sign Munnerlyn.
The move was necessitated because the Bills have placed cornerback E.J. Gaines on injured reserve with a groin injury.
Gaines, who returned to the Bills in the offseason on a one-year, $2.1 million deal after spending last season with the Cleveland Browns, was expected to miss "weeks," McDermott said this week.
Gaines suffered the injury during practice last Sunday and left the field.
He was competing with incumbent Levi Wallace and Kevin Johnson for the starting cornerback spot opposite Tre'Davious White.
The Bills also placed defensive tackle Robert Thomas on injured reserve with a knee injury.
The team signed Roderick Young, who was waived on injured reserve by the Jacksonville Jaguars in June. Young, listed at 6-1 and 307, was an undrafted free agent from North Texas, who had 134 tackles and 6.5 sacks in 48 games at the school.
The Bills also released offensive lineman Nico Siragusa, who was signed days ago. The team signed Demetrius Rhaney, who most recently played for the Hamilton Tiger-Cats of the Canadian Football League and the Memphis Express of the Arena Football League.
Rhaney, 27, is listed at 6-2 and 305 pounds. He was a seventh-round pick of the Rams in 2014, spent three seasons with the Rams and then was with the Jaguars and Redskins.
The moves bring the Bills' roster back to 91 players.