Raiders' practice squad after Matt McGloin suffered an injury in the final game of the regular season. Gilbert was to serve as the backup in case McGloin was unable to play in the Wild Card Round. McGloin ended up being active as Connor Cook's backup for the playoff game. Gilbert was not re-signed after the season. Carolina Panthers After working out with the Dallas Cowboys in January, Gilbert signed with the Carolina Panthers on March 24, 2017. He was waived on September 2, 2017, and was signed to the Panthers' practice squad the next day. He was promoted to the active roster, for the first time in his career, on October 16, 2017. After losing the back-up quarterback job to Taylor Heinicke during training camp he was waived on September 1, 2018. Gilbert was re-signed by the Panthers on December 26, 2018, after Cam Newton and Heinicke were both shut down for the season. He served as the backup to Kyle Allen in the Panthers' last game of the season. He made his NFL debut in relief of the injured Allen. He completed his first career pass to Ian Thomas for 31 yards. He finished the game with 40 yards passing. On December 31, 2018, Gilbert was waived by the Panthers. Orlando Apollos On November 27, 2018, Gilbert was drafted by the Orlando Apollos in the Alliance of American Football's quarterback draft. He played for the team during the inaugural 2019 AAF season. During the inaugural game of the 2019 season against the Atlanta Legends, Gilbert went 15 for 25 for 227 yards, with two passing touchdowns and a receiving score in the 40–6 win. He also threw the first touchdown in both Apollos and Alliance history, with a 26-yard toss to Jalin Marshall. In Week 2 of the 2019 season, Gilbert won Offensive Player of the Week with a 393-yard, two-touchdown performance in the 37–29 win over the San Antonio Commanders, and set an early AAF record for passing yards in a single game. When the AAF suspended operations after Week 8, Gilbert led the league in passing yards (2,152), attempts (259), completions (157), and passer rating (99.1). He was also second in passing touchdowns (13), second-lowest in interceptions (3), lowest in interception percentage (1.2), and second-highest in touchdown percentage (5.0) among all starting quarterbacks. After the season ended, he was named league MVP. Cleveland Browns On April 5,