McLaren are more than half a second adrift of midfield leaders Haas, according to Carlos Sainz.
Haas' Romain Grosjean qualified sixth in Australia, just two places ahead of McLaren's Lando Norris, but there was a half second gap between them.
The Spaniard believes it will be a "difficult task" for McLaren to outdevelop the American team and overtake them this season, going by what he's seen in testing and the opening Formula 1 race in Melbourne.
"Haas are a bit too far ahead in the midfield for everyone else. That is the only bad thing compared to last year, that the Haas is a bit too far away compared to last year.
"It is more than half a second," said Sainz. "To close a gap of half a second even in high development rate this season it would be a very difficult task as they won't standstill so you need to develop at least seven or eight tenths which is a lot of lap time.
"My big estimate is it is going to be very difficult to end the year in front of Haas in qualifying. I wouldn't say in a race but in pure pace it is going to be very difficult for anyone."
Asked where that figure came from and if it was based on Australia alone, or testing, Perez added: "Both. I don't look at numbers as much as the engineers, I just do my guesses looking at lap times and how good their lap times were compared to mine or my team-mate's.
"I did a rough calculation, this is not an exact number I am just giving you my guess at half a second. Half a second is a lot but we will try."
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