Collins will not accompany the Mets back to New York and will remain hospitalized in Milwaukee overnight for further examination and observation.
"Without getting into too many details, he just didn't feel good," said Mets bench coach Dick Scott, who served as acting manager Sunday. "The good thing about what we do is we have guys like [athletic trainer] Ray Ramirez and [assistant athletic trainer] Brian Chicklo right across the hallway. They came right in, followed protocol and took care of Terry right away. He actually felt fine right before the game, so we were all encouraged. Hopefully that's the case."
Mets assistant general manager John Ricco did not feel as if the concern level regarding Collins was high and said the skipper watched Sunday's game in the hospital with Ramirez.
Ramirez will stay overnight in Milwaukee with Collins.
"He was probably a bit agitated with the result, knowing Terry," Ricco said. "Other than that, he was feeling fine."
Mets starter Steven Matz said Scott informed the team of Collins' absence just before the team took the field for the game.
"It was tough," Matz said. "We're all concerned about him. I haven't heard anything, but we're worried about him."
New York was sloppy in the early going, committing a pair of errors that allowed the Brewers to jump out to a 3-0 lead after two innings.
"I just think guys are human," Scott said. "We care about the manager. It was on everybody's mind because it was so close to the beginning of the game. I'm sure we'll move on, but first and foremost, all of our concerns are with Terry right now."
The Mets have an off-day Monday before beginning an eight-game homestand. It is unclear whether Collins will be able to manage Tuesday against the Pirates.
"It is too early to tell," Ricco said. "They may release him first thing tomorrow. Then we have the off-day. That's speculation. I don't really know at this point."
Andrew Gruman is a contributor to MLB.com based in Milwaukee. This story was not subject to the approval of Major League Baseball or its clubs.