Valtteri Bottas believes that Toro Rosso won't be able to compete with Formula 1's best teams, despite qualifying on the third row for the Spanish Grand Prix.

Carlos Sainz Jr and Max Verstappen will start from fifth and sixth respectively at the Circuit de Catalunya, finishing Q3 faster than Toro Rosso's sister team Red Bull.

However, Bottas, who begins Sunday's race from fourth, believes that the Italian outfit won't challenge the fastest teams in Barcelona.

"We do not expect them to be a threat tomorrow," the Williams driver told reporters. "We think we still have better race pace than them. They have made a good step forward, but I think in the race we are stronger.

"You can never underestimate any team, but from what we see on Friday we think we should be clear of them.

"We know for sure Ferrari has quite a good edge in race pace, and they are much stronger in the race. So it is up to us with the strategy. It is a difficult circuit to overtake so maybe we can keep one of them behind."

Bottas finished fourth in the 2014 drivers' championship.