Niki Lauda believes Helmut Marko regrets his criticism of Renault, who appear to be Red Bull's only option for the 2016 season.
Failing to compete against Mercedes since the introduction of V6 engines, Red Bull publicly lashed out at engine partner Renault.
With few signs of improvement the four-time World Champions called time on that relationship, announcing that they would part ways at the end of this season.
But with Mercedes and Ferrari both refusing to power Red Bull in 2016, and McLaren vetoing a deal with Honda, Red Bull may have to fix their relationship with Renault in order to remain in F1.
"Next year, whatever the FIA does for a future engine, it will not be available," Mercedes non-executive director Lauda told Motorsport.com.
"There is no [new] engine next year, the alternative. So what I would do if I'm Red Bull? I tell you.
"Ferrari said no engine, Mercedes can't because we have four teams already. There's only Renault left.
He added: "If you ask Marko honestly, 'did you make too much negative talk in your relationship with Renault?'
"He also said to me, 'Yes.'
"All I'm trying to say is that the only alternative if Red Bull wants to continue, and I think they want to, is to find a way with Renault. It's clear."