Money was "a factor" in Mercedes' failure to succeed during his three-year comeback, Michael Schumacher insists.
The German marque openly admits that it does not spend as much on its Brackley based works team than top teams like Red Bull and Ferrari.
Schumacher told Auto Motor und Sport: "It's a factor.
"Over the years Red Bull built an infrastructure and has a budget giving them the possibility to respond to anything in the best possible way.
"It is nothing more or less than what we had at Ferrari," said the 44-year-old, who won five titles for the Maranello based team last decade.
Mercedes, never higher than fourth in the constructors' championship since the Brawn buyout in 2010, has denied it is now pumping in more funding for 2013 and beyond.
It has, however, replaced Schumacher with 27-year-old Lewis Hamilton.
Briton Hamilton has said he wants to turn Mercedes into a top team.
"I know that deep in his heart he wants to win all the time," team boss Ross Brawn is quoted by Germany's Die Welt, "but he must also understand the course of development we are on at the moment."
Niki Lauda, the new non-executive chairman, agrees: "I prefer a sober analysis of the situation rather than promising something we cannot deliver."
But Hamilton's teammate Nico Rosberg insists that, although car development appeared to stall in the second half of 2012, Mercedes is making progress.
"If you walked through the factory today, you would see a massive improvement compared to three years ago," said the German, who is six months younger than Hamilton.