The Woking-based outfit, who have both Perez and Jenson Button representing them, have failed to reach a podium spot with their MP4-28 car so far this season.
"I think we are very far from [winning]," Autopsort.com quotes Perez as saying. "We have to do big updates, big improvements.
"At the moment we are one second per lap slower [than the pace setters], so we are not in the position that we want. You don't win races by being one second off the pace."
McLaren are currently preparing for this weekend's British Grand Prix.