Gregory, who had been participating in training camp with the Kansas City Chiefs, declared his decision through a statement released through his agent, David Canter.
The 31-year-old entered the NFL as an undrafted free agent with San Diego and spent six seasons with the Chargers, making 13 starts in 2011. Gregory then signed with the New England Patriots and started 23 games over the last two years.
Gregory recorded 79 tackles and one sack in 14 games with the Patriots last season. He was released by New England in February and signed with the Chiefs at the start of training camp.
Over 111 career games, Gregory compiled 357 tackles, seven interceptions, 25 passes defensed and three sacks.