Sebastian Vettel is confident former team Red Bull will be fighting for wins in Formula 1 sooner rather than later.

The team with which the German won his four world titles has had a disappointing start to the 2017 season, with Max Verstappen scoring their only podium so far in China.

Ahead of the next race in Spain, however, there's anticipation a major upgrade, considered by some as a B-spec RB13, will see Red Bull close what was a near two-second gap to the front in Sochi. 

"It will be a surprise, I think it will be a very close race between Mercedes and us, I hope, and I also hope that Red Bull find some pace," Vettel said, looking ahead to Barcelona.

"There's a lot of rumours around. They are a strong team, they know how to build a quick car so I expect it's a question of when rather than if [they close the gap]. But the sooner, the more exciting it will be.”

The issue the Milton Keynes-based outfit face is the goalposts they are aiming for are also shifting, with Vettel sure his Ferrari team is capable of making their own performance gains.

"For us, I'm confident that we have the right people, the right tools on board and we will make progress,” he claimed. “It obviously depends on what others are doing.

"We had a good run up in Barcelona at the tests, so looking forwards to [the race at] Barcelona, the car feels good. I think we've improved it from early March to now, I think we've had a very good start.

“It would be wrong to sit here and say that's what we expected -- but we're here to win, we're here to do our best. If we look back I think we have more or less extracted the maximum.”

Vettel is also refusing to dwell on a disappointing second to Valtteri Bottas’ Mercedes in Russia, despite some critical remarks towards Felipe Massa post-race.

"[I’m] So very happy with where we are as a team but we can still learn and we can still improve and I think that's the way we go forward,” the four-time champion reflected.

“Nothing is for granted, Barcelona is just another race and we have a lot of races to go this year. But before that we have two weeks' time to look at what we have done so far and improve.

"In Russia I think the speed in general was there, the balance dropped away from me a little bit in the first stint. I struggled with the fronts and couldn't attack as much as I was hoping for and as much as I was probably able to in qualifying.

“So things that we could have done better but the race is done today so yeah, I'm generally looking forwards: we have a strong car, a strong team, the spirit is good, so lots of positives."