Sergio Perez believes that Mercedes' rival engine manufacturers will catch up with the teams running the German units before the start of the 2014 Formula 1 season.
Mercedes has so far appeared to have the strongest of the new powerplants this year, prompting suggestions that its customer teams will be able to capitalise on the struggles of Renault teams in particular when the season starts.
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But Perez, whose Force India uses Mercedes power, is not expecting the field to be divided by engines by the time of the Australian Grand Prix next month.
When asked by AUTOSPORT if Mercedes would have an advantage in the early races, Perez said: "I think the others will come back earlier than the first race.
"The Mercedes is working fine, it seems reliable. But things are going to change.
"I'm sure we will see the other manufacturers come back and it will be a very close battle between the front and the midfield."
Perez pointed to the delay encountered by Force India at the start of Friday's running - caused by overnight work taking longer than expected - as evidence that even the Mercedes teams are not in the clear in terms of reliability.
"The other teams are having issues, but everyone is at the moment," he said.
"Even us, this morning we had a big delay of two hours so we didn't manage to complete the full programme.
"Other teams are struggling in the same way, so it's difficult."
When asked if the form of the VJM07, which topped the times with Nico Hulkenberg earlier this week, was looking good ahead of the season, the former McLaren driver said: "I wouldn't draw that conclusion yet.
"We are definitely doing good work before Melbourne, which is the target. We will see what we can do before the first race."