The Broncos announced in a statement Monday that Kubiak was "feeling much better," although they did not reveal whether he would return to coach the reigning Super Bowl champions in Thursday night's game against the San Diego Chargers.
Kubiak was taken by ambulance to the hospital Sunday night after the Broncos' 23-16 loss to the Atlanta Falcons. He coached through the end of the Broncos' first loss of the season, even though he had felt ill during the game, according to team officials.
Kubiak did his customary news conference after the game and walked back into the locker room. He continued to feel ill, however, and was taken by ambulance to the hospital.
"After experiencing flu-like symptoms following Sunday's game, Denver Broncos Head Coach Gary Kubiak underwent several precautionary tests at the hospital," the team's statement said. "These included an MRI and CT scan, both of which came back normal.
"Coach Kubiak was diagnosed with a complex migraine condition that caused extreme fatigue and body weakness. He received medication and is feeling much better with an expected release from the hospital this afternoon."
John Elway, the Broncos' executive vice president of football operations and general manager, is expected to update Kubiak's condition as well as the team plans for the week later Monday afternoon.
If Kubiak does not make the trip against the Chargers, Broncos defensive coordinator Wade Phillips is a former head coach, offensive coordinator Rick Dennison is a longtime assistant and running backs coach Eric Studesville served as the Broncos' interim coach in 2010 after Josh McDaniels was fired.
In 2013, Kubiak suffered what was described as a mini-stroke at halftime of a game against the Indianapolis Colts. He spent two nights in the hospital after that incident.