McKeon, who makes Elon, N.C., home, typically visits Spring Training camp for a couple of weeks.
The 82-year-old, of course, managed the franchise to the 2003 World Series championship.
Current Miami manager Mike Redmond was part of that team, and he played two seasons for McKeon.
Early Tuesday, McKeon walked into Redmond's office and proclaimed: "I'm reporting for duty."
McKeon was supportive of the Marlins hiring Redmond, who replaced Ozzie Guillen.
Redmond finds a benefit to having McKeon, and his 60-plus years of professional experience, around the youthful team.
Redmond noted that as a manager, McKeon had loyalty to his players.
"He played those guys. He stuck with them," Redmond said. "It didn't matter if you were struggling, and you were 0-for-20, he'd run you out there. He'd keep running you out there until you figured it out.
"At the same time, too, he was able to get the bench guys all on board with what we were trying to do. He made everybody accountable. Everybody was accountable for their job, and their role on the team. And it worked. He had a lot of success."