Gary Kubiak in hospital after collapse

Those in touch with Gary Kubiak's family said Monday morning that the Houston Texans coach is "feeling good" after he collapsed at halftime of his team's game against the Indianapolis Colts on Sunday night.

Kubiak, who has been at a Houston hospital since Sunday night, was treated with an IV medicine -- tissue plasminogen activator (tPA) -- designed to break up blood clots, per medical sources.

Doctors are conducting tests Monday to determine whether he suffered a stroke.

The Texans are uncertain when Kubiak, the team's coach since 2006, will return. They said in a statement released Monday that he will remain in the hospital for at least the next 24 hours.

"Our primary concern is of course with Gary's health and well-being," Texans general manager Rick Smith said in the statement. "There have been so many people throughout the city and across the country that have reached out to express their love and support, and we are thankful for everyone's thoughts and prayers. Gary is alert, coherent and in good spirits. He is continuing to be evaluated and monitored."

"We're still worried about Kub, making sure he's OK," inside linebacker Joe Mays said Monday after practice. "We want him back here, but it's a process he has to go through. At the same time we know there's still work to be done. We wanted to come in and go to work as usual and fix the mistakes that we have."

The 52-year-old Kubiak fell to his knees and grimaced when he collapsed, but he never lost consciousness.

Kubiak lay on the ground for several minutes and was surrounded by medical personnel, including Texans head trainer Geoff Kaplan. After a few minutes, Kubiak sat up and spoke with those surrounding him before eventually being strapped to a stretcher and taken off the field.

Defensive coordinator Wade Phillips took over in the interim. Houston led the Colts 21-3 at halftime but wound up losing 27-24.

Phillips ran practice and meetings Monday, but the Texans said there has been no decision on whether Kubiak will coach Sunday at Arizona. The team also said no decision has been made on who would take over for Kubiak if he can't coach.

"I think we are in great hands with whoever has to step up," Mays said. "We have a great group of coaches, we have a great group of players. At the end of the day, we're going to go out and play great football. That's how I feel about it."

In Eden Prarie, Minn., Vikings coach Leslie Frazier said Monday that Kubiak's son, Klint, who is an offensive quality control coach for Minnesota, left the team to be with his father.

ESPN.com Texans reporter Tania Ganguli contributed to this report.