"We have been looking (at F1), but even with all the new teams coming in, it's not easy to get a race seat," the Brit told Autosport.
"It seems like most of the new teams require you to have a fair few million pounds in the bank, or that much sponsorship to give the team, so it's more difficult to get a race-seat even though there's more available.
"The teams are struggling budget-wise and it's not easy to lay your hands on a lot of money. We've been looking at opportunities, but there don't seem to be that many available."
The slim chances of landing a F1 drive mean the 2005 DTM Champion is contemplating another season in the series, while continuing in his role as McLaren test driver.
"I'm focusing on what I've got at the moment," he said. "I've had a great year in DTM with Mercedes and we're looking at probably doing that again – continuing with them and trying to get the Championship back for them after three years without it.
"And also continuing my work with McLaren. I've been with them full-time since 2005 and I hope to build on that and hopefully become a more integral part of the team.
"It's been great working with them and with Lewis (Hamilton), and now with Jenson Button on board, it will be great working in a team with two World Champions."