(CNN) -- Houston Texans head coach Gary Kubiak will remain hospitalized for at least one more day after collapsing as he walked off the field for halftime of the team's Sunday night game against the Indianapolis Colts, the team said Monday.
"Gary is alert, coherent and in good spirits," the team said in a statement. "He is continuing to be evaluated and monitored."
The Texans didn't elaborate on what might be wrong with Kubiak, who "experienced dizziness and a light-headed feeling" before sinking to the ground, according to the team.
On Sunday, defensive coordinator Wade Phillips said the coach "did not have a heart attack, but they're still checking on everything with him."
The 52-year-old coach was walking near the 20-yard line just after halftime started when he slowly bent over and then collapsed, shocking the audience and members of Kubiak's own team and staff.
In a post-game news conference, Phillips recalled his confusion in the moments after Kubiak's collapse, describing it as "a shock to everybody."
"I was traveling in, and I saw him on the ground, and I kept asking, 'What happened?' " he said. "And that's kind of what happened with everybody."
'It looked serious'
One Texans player, defensive end Antonio Smith, said he saw Kubiak collapse.
"He went down to his knee and couldn't get back up and looked like he was having trouble breathing," he said after the game.
"It looked serious because he couldn't get back up and everyone was surrounding him."
Kubiak was tended to by a flock of medical staff as he lay on the field. He was eventually wheeled out on a stretcher.
"We finally got word that they took him to the hospital, but we were unsure of everything," Phillips said.
Concern from both teams
The Colts went on to win the game 27-24, even though the Texans led 21-3 at halftime. But Phillips refused to use Kubiak's collapse as an excuse for the defeat, saying Houston had opportunities in the second half.
"When the game was on the line, we didn't play well enough," he said.
"We were very concerned at halftime," Texans tackle Duane Brown said. "We actually were more motivated if anything to try to go out and get the win. But once we were out there and started playing again, it didn't stick around in our minds too much."
Houston's opponents also voiced their concern about Kubiak. Colts owner Jim Irsay offered his support to the Texans coach.
"Big time prayers for Coach Kubiak," Irsay tweeted. "God bless his healthy return and ease his family's worry and concern."
Star defensive player J.J. Watt said after Monday's practice that players had yet to talk with the coach. He said he hadn't noticed anything of concern with Kubiak in the days leading up to Sunday's game.
He described his coach as hard-working.
"His truck's always the first one here and the last one to leave," Watt said. "The guy lives for it, and he lives and breathes this game. He puts it all out there for us, and obviously we hope to get him back soon."
Kubiak is among a number of football coaches to suffer dramatic health issues recently.
Denver Broncos head coach John Fox was taken to a hospital Saturday after feeling lightheaded while playing golf, the team said, and he underwent "successful" surgery Monday to replace an aortic valve. He will be away from coaching for at least the next several weeks, the team said.
In September, University of Minnesota Gophers head coach Jerry Kill suffered an apparent epileptic seizure on a sideline at halftime, the sports website Bleacher Report said at the time.
Kill, who has a history of such seizures, has been on leave as head coach since October 10 but continues to be involved with the team while receiving treatment to manage his epilepsy, the school said in a statement.
CNN's Joseph Miller, Jake Carpenter and Joe Sutton contributed to this report.