MILWAUKEE — Mets manager Terry Collins remained overnight at a local hospital for observation and more tests after falling ill about 30 minutes before Sunday’s 5-3 loss to the Brewers.

When asked about his level of concern, assistant general manager John Ricco said, “I don’t think it’s high.” The team did not disclose Collins’ precise symptoms.

The Mets traveled back to New York for a scheduled day off Monday while Collins stayed behind in Milwaukee along with team trainer Ray Ramirez.

“They were watching the game, I know that,” Ricco said after the team’s sloppy loss. “He’s probably a bit agitated, knowing Terry. But other than that, he’s feeling fine.”

It’s unclear whether Collins will manage the Mets’ next game Tuesday against the Pirates.

Collins, 67, is the oldest manager in the big leagues. He had not complained of any issues earlier in the day and his illness caught team personnel by surprise.

Before managing the game, bench coach Dick Scott called a brief team meeting in the clubhouse about 30 minutes before first pitch to announce that Collins had left the team.

By then, the manager had complained of feeling ill and was seen by medical personnel at Miller Park. He then showered and walked out of the Mets’ clubhouse under his own power, headed for nearby Froedtert Hospital.

“I was just with Terry,” Ricco said just before the game began. “He was alert and fine. Just wasn’t feeling well before the game, so we’re going to have some tests run . . . We’re just being cautious.”

Curtis Granderson said that aside from Scott’s announcement, players received little information about Collins’ condition. He insisted it did not impact the team’s play, but Scott acknowledged that it might have been a factor in the Mets’ uncharacteristically sloppy loss.

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“First and foremost,’’ Scott said, “all of our concerns are with Terry right now.”