Honda sponsored ITV1's 2007 coverage in a deal thought to be worth £2.5m, but advertisers have so far failed to commit to a higher deal for the 2008 season.
Tim Brady, managing partner at Newcast, ZenithOptimedia's branded content division, said: "It's a high price. The problem is that it's a very repetitive audience."
An ITV spokesman said: "We are currently in discussion with a number of parties and are confident we will secure a sponsor soon."