Bob LaMonte said Weis came down with an infected gall bladder Friday, but elected to wait until after the game against the 49ers to have surgery.
"He didn't bother to do anything other than live through 48 hours of pain," LaMonte said. "He knew he was coaching on Sunday."
Weis checked himself into a Kansas City hospital Monday morning, and LaMonte said the coach is expected to be released Tuesday. The Chiefs have a bye week after winning their first three games of the season, and LaMonte said Weis should be recovered in time for a Week 5 showdown with the Indianapolis Colts.
Weis, 54, coached throughout Sunday's game. A local radio station, 810 WHB, cited unidentified sources as saying Weis was taken to a hospital for an undisclosed illness shortly after the game.
Haley refused to say whether or not Weis was taken to a hospital.
"As is my policy, I won't talk about anybody's ... health ... that's a family business deal," Haley said Monday. "That being said, there's nothing life-threatening, heart attack-related, any of the couple of things that have been brought to my attention regarding Charlie. I will make that statement just to keep there from being a bunch of hoopla. I won't get into the personal side with any of our associates, employees, coaches, players."
Weis underwent knee surgery during the offseason and spent most of training camp moving around on a motorized cart and walking with difficulty while using a cane and wearing a large knee brace. All he has said about that situation was that part of his knee "fell off" a few weeks before camp opened.
The Associated Press contributed to this report.