Jean-Eric Vergne has explained the reasons behind Red Bull's decision to overlook him for a Formula 1 seat in 2015 despite being told he would get a drive if Sebastian Vettel left the team.

Vergne made his F1 debut with Toro Rosso in 2012, but was told in the summer of 2014 that he would be losing his seat for 2015 in favour of Max Verstappen, who would race alongside Daniil Kvyat.

Vettel dropped a bombshell over the Japanese Grand Prix weekend by announcing his decision to leave Red Bull, with the team immediately deciding that Kvyat would be getting the seat, leaving a space free at Toro Rosso. This drive was eventually taken by Carlos Sainz Jr.

Vergne had been told by Red Bull he would get Vettel's seat if the German decided to leave the team, only for it to go back on the decision, with the Frenchman ultimately moving into Formula E.

"In the summer I got a call from Red Bull saying that they would put Max in the car. Back then, I totally understood it," Vergne told

"It was like, OK, Toro Rosso is some kind of school for the Red Bull junior drivers and there was no place to go to Red Bull, so actually it was kind of them to let me know so early in the season.

"But during that call, I said: 'What if Vettel goes?'. He said: 'You will be in the car'.

"I had done a great season so far, it was good. They knew the deficit I had against Kvyat in the car, talking about the weight [disadvantage]. Later on, when Vettel left, it was after my good races that I had done.

"But I found out later that because the way it was said, it would have looked bad that they'd come back on that decision.

"It was a frustrating situation, definitely. Then the whole Toro Rosso team wanted to keep me next to Max, and at the end of the day, it was the same outcome. They would not go back on the decision."

Vergne joined Formula E just weeks after his final F1 race, where he continues to drive with the Techeetah team. He also now races in the FIA World Endurance Championship with Manor.