Marlins manager Mike Redmond and outfielder Juan Pierre played for McKeon, and they were part of the 2003 World Series title team.
"I just told him I was thinking about him, and I was praying for him, and I hope everything goes well," said Redmond, who spoke with McKeon a few days ago. "I'm sure everything will be fine.
"Jack is such a big part of my life. He's touched so many guys in this game. You look at Jack, and you think of this guy as invincible."
Pierre was the catalyst of the '03 Marlins, leading off and playing center field.
"He's the ageless wonder," Pierre said. "You're used to seeing him walking around with that cigar, every day. He never seemed to get old. Hopefully, it's something that isn't too serious, and he will be back to his old self."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter