New York Mets manager Terry Collins (10) looks on during...

New York Mets manager Terry Collins (10) looks on during warmups before Game 2 of the World Series against the Kansas City Royals at Kauffman Stadium on Wednesday, Oct. 28, 2015. Credit: Newsday/ William Perlman

After spending Sunday night in a Milwaukee hospital, Mets manager Terry Collins was released on Monday, the club announced. He’s expected to be in uniform for Tuesday night’s series opener against the Pirates at Citi Field.

Collins, 67, left Miller Park about 30 minutes before first pitch on Sunday. He had complained of feeling ill, though the precise nature of his symptoms were undisclosed.

When asked on Monday about his condition, Collins texted simply: “A-OK.”

According to the Mets, Dr. Brian-Fred Fitzsimmons cleared Collins to return after all tests came back negative. Collins, the oldest manager in the big leagues, had been kept overnight for tests and further observation.

The Mets had been encouraged by the fact that Collins had not complained of any other symptoms before falling ill prior to the game. Even then, he was said to be in good spirits. He walked out of the Mets’ clubhouse under his own power on the way to the hospital.

He was accompanied by trainer Ray Ramirez; assistant trainer Brian Chicklo remained with the team.

Bench coach Dick Scott took over managerial duties during the Mets’ 5-3 loss to the Brewers, a sloppy affair in which the club might have been distracted by Collins’ absence.

Most players did not know that Collins had fallen ill until Scott abruptly called a brief clubhouse meeting to make the announcement.

“Without getting into too many details, he just didn’t feel good,” Scott said after the game. “The beauty of what we do is we have guys like Ray Ramirez and 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.”

With Ramirez at his side, Collins was said to have watched Sunday’s three-error defeat, marking the end of a 10-game road trip in which the Mets went 5-5.

Righthander Jacob deGrom (3-2, 2.80 ERA) will start against Pirates righty Juan Nicasio (5-5, 5.34 ERA) in the opener of a three-game series against the Pirates. DeGrom could have started on Sunday instead of lefthander Steven Matz, but when deGrom emerged from his previous start with more soreness than Matz did, Collins elected to bump him to Tuesday, allowing for extra rest.

The Pirates (32-31) have dropped five straight. Like the Mets (34-28), injuries are beginning to pile up.

The Pirates recently lost starting catcher Francisco Cervelli for four to six weeks after he had surgery to repair a broken bone in his left hand. Staff ace Gerrit Cole soon could be placed on the disabled list with right triceps tightness.