Darby tore his ACL in November. While other teams reportedly offered him multi-year pacts, he opted to sign a prove-it deal with hopes of cashing in next offseason, according to NFL Network's Mike Garafolo.
The 25-year-old may not be ready for the start of the regular season, notes Rapoport.
Darby, a former second-round pick of the Buffalo Bills, was considered one of the top defensive backs on the market despite his knee injury. He racked up 43 tackles, 12 pass defenses, and one interception before being hurt in Week 10.