The Dutch driver, who won his fourth title in a row last year, has a contract to 2028 but is wanted by both Mercedes and Aston Martin and has performance clauses that make an early exit possible.
Verstappen's importance is fundamental. The most sought-after driver on the grid is an absolute number one in a team struggling to find anyone else who can get even close to him on the track.
The champion has scored 165 of his team's 172 points in 12 races so far this season and has had three teammates in less than a year.
But he is only third in the championship, his hopes of a fifth crown this season receding fast with a hefty 69 points now between him and McLaren's leader Oscar Piastri.
If Verstappen leaves, whose seat does he take? Will it be his old Mercedes foe George Russell or Italian 18-year-old rookie Kimi Antonelli? And where will they go?
Horner had once been seen as the glue that bound a winning team, the young leader of a group whose success confounded those who dismissed them as just an energy drink brand, and shook up the sport.
Then, after Red Bull won eight drivers' titles and six constructors' championships and 124 races, the empire began to fall apart.
The death of Red Bull co-founder Dietrich Mateschitz in October 2022 removed a key pillar of support for Horner and led to reports of a power struggle between the team's Austrian and Thai owners.
Then in early 2024, after the most dominant season in the sport's history with Red Bull taking 21 wins in 22 races and Max Verstappen the third of his four titles, Horner faced allegations of misconduct from a female employee.
He denied them, and was cleared after an investigation, but that was not the end of the story for a man in office since 2005, the only principal Red Bull have had since entering the sport as constructors.
Some paddock regulars called time on Horner even then, seeing his position as untenable, but the 51-year-old pulled through and seemed to have cemented himself back in position.
Married to Spice Girls singer Geri Halliwell, Horner enjoyed his own celebrity and has been a main man in the popular "Drive to Survive" Netflix docu-series, ever combative with sparring partner Toto Wolff at Mercedes.
Verstappen's father Jos was in the opposing camp.
He called for Horner to go, saying his presence would tear the team apart, and Adrian Newey the star designer who has won titles with multiple teams announced his departure to Aston Martin.
Sporting director Jonathan Wheatley left to become principal of Sauber, guiding them to the podium with Nico Hulkenberg at Silverstone last weekend, and aerodynamics head Rob Marshall joined now-champions McLaren.
--Reuters--
