The British-based team's managing director Jonathan Neale told reporters on Wednesday ahead of the Belgian Grand Prix that it would be a tall order to expect to see Jenson Button or Mexican Sergio Perez on top of the podium before 2014.
"I think that will be a real challenge, if I'm honest," he said.
"We're almost through August and there is a lot of work to be done to get ready for next year, so I think inevitably we'll increasingly start to focus on 2014."
Formula One is introducing a new V6 engine next year with energy recovery systems and the change is one of the biggest the sport has seen in decades.
Button, the 2009 champion with Brawn GP, has not finished higher than fifth in 10 races so far this season while Perez's best is a sixth place.
Despite the slump from having the fastest car at the end of last season, Button told reporters before last month's Hungarian Grand Prix that he felt the team could still win a race and Sunday's race at Spa would be the best chance.
Button won the race from pole position last year but Neale said he wanted to 'underplay' the Briton's words.
"I think his euphoria was that he could still see the leaders for a greater proportion of the time in the last few races we've been to," he said.
"Spa is a fantastic place, drivers are always excited to get there and we love it as well, but it is notoriously difficult," said Neale. "I don't think anyone would go feeling confident."
Button and team principal Martin Whitmarsh also put some distance between them and the optimism of Hungary in a pre-race preview.
Whitmarsh said the team were "not contenders for outright victory this time round" while Button declared that "we don't go to Spa with the package to win".
McLaren, the second most successful team after Ferrari in terms of championships and race wins, last went through a season without a victory in 2006.
(Reporting by Alan Baldwin, editing by Pritha Sarkar)
