It would leave Denver searching for another head coach just two years after hiring Kubiak, who helped lead the Broncos to a Super Bowl title last season. The Broncos (8-7), who were eliminated from playoff contention last week, close their season Sunday at home against the Oakland Raiders.
This year has taken a toll on Kubiak, 55, and his family. Kubiak left the team for a week in October and missed a Thursday night game in San Diego for what the team called a "complex migraine condition." Back in 2013, when Kubiak was coaching the Houston Texans, he suffered a mini-stroke during a game and had to be rushed to the hospital.
Physically, the demands of the job have become too risky for Kubiak, according to sources.
Asked Friday about his future with the team, Kubiak was noncommittal.
"You guys know, I love this league, I love the Broncos, I love the work," Kubiak told reporters. "I'm all-in on the Raiders right now. There will be time for reflection and all that stuff next week, but right now it's time to focus on what we're doing."
Kubiak's plans will be finalized next week. The move might come as a surprise to many around the league, but there have been whispers throughout the year that Kubiak's family wanted him to leave coaching and move to their retirement ranch in Texas.
Both Kubiak and general manager John Elway, his former Broncos teammate, believed it was going to be a long and prosperous return. Instead, Kubiak is expected to step down as Broncos coach after Sunday's regular-season finale against the Oakland Raiders.
Kubiak's Broncos went 12-4 in his debut season, in which he guided Denver to a Super Bowl win over the Carolina Panthers.
In addition to leading the Broncos to their third championship, Kubiak won two Super Bowl rings in Denver as Mike Shanahan's offensive coordinator in 1997 and 1998.