The Lions traded Diggs, along with a 2021 seventh-round draft pick, to the Seahawks on Tuesday in exchange for a 2020 fifth-round pick.
Diggs, 26, said Wednesday that he was "blindsided" by the trade and several of his teammates shared their stunned reactions on Twitter on Tuesday, highlighted by cornerback Darius Slay, who called the move "bulls---."
Gilchrist, 30, was one of the bright spots on an oft-porous defense for the Oakland Raiders in 2018, tying for the team lead with a career high-tying three interceptions.
After signing a one-year free-agent deal last spring, Gilchrist started all 16 games for the Raiders at either safety or nickel cornerback. His 56 tackles (38 solo) led the team's secondary as he also had six passes defensed, one off his career best.
And despite being an older veteran, Gilchrist also played special teams.
Gilchrist, a second-round pick (50th overall) in the 2011 draft, joined the Raiders after four seasons with the Chargers, two with the Jets and one with the Texans. For his career, he has 14 interceptions, 497 tackles, five forced fumbles and a recovery.