UPDATE, 3:42 PM: Gagnon has been DFA'd by the Mets.
With 37 players on the Mets' 40-man roster and the team needing to add certain prospects to the roster by Nov. 20 to protect them from the Rule 5 Draft (as well as soon needing to add expected additions from free agency and/or trades), Gagnon's roster spot with the Mets could have been in jeopardy.
Gagnon is technically under Mets control through the 2024 season and isn't eligible for arbitration until the 2021 season, so any deal to let him leave to pitch in the KBO would require the Mets' approval.
The 29-year-old Gagnon made 18 relief appearances for the Mets in 2019, posting a 8.27 ERA (8.96 FIP) and 1.73 WHIP in 23.2 IP.
In Gagnon's worst appearance of 2019, he allowed four home runs in 1.2 IP against the Braves on Aug. 15.
Gagnon's overall performance in 2019 wasn't much better than how he fared in 2018, when he had a 5.25 ERA (5.74 FIP) and 1.66 WHIP in 12.0 IP (four relief appearances, one start).