Sebastian Vettel: Ferrari driver says Red Bull-Renault split is 'sad'

Sebastian Vettel won four consecutive drivers' world titles with Red Bull-Renault from 2010-13

Ferrari's Sebastian Vettel says he is "sad" to hear about the impending divorce between his former Red Bull team and engine partner Renault.

Vettel, who won four consecutive Formula 1 titles with Red Bull-Renault, said the success they achieved together "unfortunately gets forgotten".

Renault say they will soon stop providing engines to other F1 teams.

"Renault did a fantastic job supplying with a strong engine and the latest technique," Vettel said.

"When we had the era of blown exhausts, Renault was one of the best and most advanced. There are a lot of things Renault has achieved that people tend to forget. I hope they stay in the sport."

His remarks, which will be seen by some as veiled criticism of Red Bull, are a reference to a now-banned technology known as exhaust-blown diffusers, in which Red Bull and Renault excelled from 2010-13.

This was the harnessing of exhaust gases with aerodynamic design at the rear of the car to dramatically increase rear downforce and therefore cornering speed.

Red Bull and Renault were standard-setters in this technology and used it to devastating effect over the four years in which they won both the drivers' and constructors' titles.

But Red Bull's patience with Renault has snapped after the company failed to get to grips with the new turbo hybrid engines that were introduced into F1 in 2014.

Their relationship has grown increasingly tense after a series of public criticisms of Renault by Red Bull management.

Red Bull and Renault have not yet formally admitted that they are to split, despite having a year still to run on their contract.

But Renault boss Carlos Ghosn has said they are "renegotiating" the contract and Red Bull have admitted they are exploring their options by talking to other engine manufacturers.

Red Bull motorsport boss Helmut Marko has said their hopes of getting a Mercedes engine in 2016 are over and Ferrari have said they are prepared to supply the team.

It is considered an open secret in F1 that Red Bull will use Ferrari engines next season.

Renault are considering becoming a constructor in their own right again and are in talks aimed at taking back control of the Lotus team, which the French company sold to investment group Genii Capital at the end of 2009.

Ghosn says no final decision has yet been made and that Renault will pull out of F1 if it does not take over a team.