Jenson Button admitted that despite a raft of new parts from the McLaren team he remained "a hell of a long way off the pace" in practice for this weekend's Spanish Grand Prix.
After struggling to compete in the four season-opening 'flyaway' races in Australia, Malaysia, China and Bahrain, the 2009 world champion had hoped he and McLaren would be back with a bang at the Circuit de Catalunya.
But after the the opening two free practice sessions, he admitted that the progress that McLaren had made in improving the car had been lost by the equal progress made by their rivals.
The 33-year-old Briton said: "Its great that we're able to turn things around so quickly in terms of bringing parts to the circuit, but we're still a hell of a long way off the pace.
"There are some positives to the parts, but some areas we need to improve on -- areas I didn't think we would have to! We haven't slipped back, we've made improvements, but I think everyone has...
"The important thing is that the correlation (between our simulated performance and our track showing) is much better now, which is a positive, definitely for the future.
"I think (on Sunday) you'll see four teams that are very competitive at the front. I don't think we'll be one of them -- but I think we'll be just behind hopefully."
Button added that the mixed weather conditions during FP1 and the need to focus on long runs to check tyre performance reduced the time available to test new parts properly.
"The problem is we've hardly tested," he said. "Its not perfect conditions (and then) it's basically been doing long runs seeing what the tyres will do," he explained.
"We still don't have the outright pace of the quick guys as everyone is moving forward. We need a big chunk and I'm not sure we have that. I think we can improve overnight, but we're not there yet."
Button wound up 12th in practice with teammate Sergio Perez in 13th.