Morgan, who plays Negan, fielded questions from Walking Dead fans aboard Walker Stalker Cruise when he was asked about considering a return to the long-running CW series.
"We're not talking about Supernatural," Morgan teased. "I mean, when Kirkman kills Negan, I'll go back to Supernatural."
Kirkman said "Then I'll never do it!"
"There we go! Never going back," Morgan joked. "No, if that show ever ends and they're on like season 400, I said I would love to go back and have some resolution with that character."
Morgan played a pivotal role on Supernatural as father of Hunter brothers Sam (Jared Padalecki) and Dean Winchester (Jensen Ackles), appearing in a dozen episodes between 2005 and 2008.
"I'll tell you this much, I'd kill Negan tomorrow if I could get more Magic City," said Kirkman, referring to the short-lived STARZ period crime drama that starred Morgan as a Miami hotel owner in the late 1950s.
"Yeah, by the way, I really enjoyed doing that character, but thank you," Morgan said. "I don't think there's any chance of it coming back though. [laughs]"
Kirkman, laughing, said, "Why don't I kill Negan and see?"
Morgan, still a recurring guest at Supernatural conventions, opened up during last year's con about the importance of John's return to Supernatural, bringing closure to his monster hunter sons.
"Before it's all said and done, and we talk about it all the time and I've been saying it for years — because it's Supernatural, and you can come back, as proven by every actor that's ever been on the show, I certainly hope that at some point not only will John return in some capacity but I think that Sam and Dean need to have some closure with this guy," Morgan said.
"And I think that John would like the opportunity to have some closure, and I think you, the audience, deserves it."
John disappeared before later reuniting with his sons as they sought to kill the demon Azazel, only for the Winchester trio to be caught in a devastating car wreck. John, making a deal with the demon to spare Dean's life, was sent to Hell. John later escaped and his spirit helped Dean kill Azazel before finally moving on.
Supernatural, now in its 13th season, airs Thursdays at 8/7c on The CW. The Walking Dead returns to AMC with its mid-season premiere Sunday, February 25.