Ralf Schumacher believes Red Bull will 'sink into mediocrity' if Christian Horner stays following news of Adrian Newey's departure.
It was confirmed on Wednesday that Newey will leave his role as chief technology officer at Red Bull Racing in the first quarter of 2025.
Red Bull have had another superb start to the season on the track, with Max Verstappen winning four of the opening five races.
But issues away from racing have stolen the headlines and led to speculation over the future of senior members of staff.
F1 news: Ralf Schumacher expects a bleak future for Red Bull after Adrian Newey's exit
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Horner was cleared of any wrongdoing following an independent investigation into allegations of inappropriate behaviour towards a female colleague.
He faced calls to resign from the likes of Jos Verstappen, father of the three-time back-to-back world champion.
Verstappen junior has been linked with a shock move to Ferrari, despite having a contract until the end of the 2028 season.
The future of the long-serving Red Bull director Helmut Marko has also been thrown into doubt.
Red Bull last week dismissed reports that Newey was set to leave but have now confirmed he will depart.
Schumacher doesn't blame the designer for leaving and reckons more will follow him out of the door.
The former driver told Sky in Germany: "Adrian Newey needs harmony, he needs a good atmosphere, a good workplace.
"And, at the moment, you have to say clearly: Red Bull is falling apart.
"The sole responsibility for this lies with Christian Horner, who is holding on to power with all his might.
"I don’t think that will be the last problem he will have when Adrian Newey leaves him.
"Max Verstappen is already thinking about it too, as is Dr. Helmut Marko, if you watch him like that."
Horner has continued in his role as normal since the allegations against him surfaced in early February.
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F1 news: Adrian Newey and Christian Horner have worked together at Red Bull for almost 20 years
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Schumacher says there have already been signs that Red Bull will struggle in the absence of Newey.
And he reckons it will only get worse if Horner stays at team principal in the coming years.
Schumacher added: "We remember last year when there were problems.
"[Newey] was ill once and then you immediately saw what was going on with Red Bull. Max Verstappen had difficulties.
F1 news: Ralf Schumacher has been heavily critical of Christian Horner in recent months
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"If he wants to continue, he has to be free. Otherwise, of course, he will still be blocked and won’t be able to work for a new team.
"I give Red Bull two more years and if they continue to hold on to Horner, the team will sink into mediocrity. I’m pretty sure of that."