Carlos Sainz thinks it will be difficult for Toro Rosso to compete for a place in Q3 at the Australian Grand Prix as its rivals have made "massive steps" over the winter.
Toro Rosso hopes to push itself up the pecking order this season after finishing seventh in 2016. Winter testing was a mixed affair for the team, with Renault reliability issues hampering the opening week, though it recovered to finish third on the final day.
Many are predicting a tight fight behind the top three -- who may be up to 1.5s ahead come Melbourne -- and Sainz thinks Toro Rosso will struggle to make the top-ten qualifying shootout at the opening round as a result.
"I honestly think that the others have done also massive steps -- Force India, Haas, Renault in particular, compared to last year," Sainz said. "Williams is flying.
"So it is going to be a very very tight fight for P5 in the championship, or to be the fifth-fastest car in Melbourne -- so to get into Q3 will be extremely difficult."
Williams was one of the stand-out performers of the second week, recovering from a problematic opening test and impressing many observers in the paddock.
When asked if he felt Williams is clearly fourth in the current pecking order, he replied: "I don't know, it's probably a bit too early to know. But they are definitely very strong and they will be very difficult to beat."