Toro Rosso's Carlos Sainz Jr believes the midfield battle will be toughly contested as other teams have made "massive steps" from 2016.
The Spaniard finished P3 on the final day of testing in Barcelona to show that Red Bull's junior team do have the potential to compete, but he believes it will be very difficult to accumlate points due to an increase in competition.
"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."
Asked whether he thought Williams were clearly the best of the rest in the pecking order, Sainz added: "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."