Jenson Button admitted feeling deflated after qualifying 17th for the Belgian Grand Prix with a lap he felt was as good as the one which earned him pole at Spa in 2012.

With a back row start already confirmed ahead of qualifying due to engine change penalties McLaren was hoping to see signs of improvement from its upgraded Honda power unit. However, that step up failed to materialise as Button crossed 17th two seconds off the pace.

"You've got to give it your all really," Button said. "We didn't have to qualify because we're going to start the race at the back. We go out there to see what we have and to try and enjoy it. I did enjoy qualifying and with my lap I felt like I got everything out of the car. I felt it was as good as my pole position lap here in 2012 and you cross the finish line and you see you're a second slower than the guy front."

Button says the team's lack of pace in Q3 was frustrating and not helped by Sauber's improved Ferrari engine, which it finally has this weekend after it was upgraded in Canada.

"It's puzzling and obviously disappointing. It's not just me who's disappointed, it's the whole team. You know, you always hope for more but it was always going to be a tricky race this one. I think the cars in front have gained a lot, they've done a good job here with the cars. But also Sauber for example have a big boost of power from their [upgraded] engine, which elevates them and hurts us as well."

With Sunday looking like another extended test for McLaren and Honda Button offered a bleak prediction of what he and team-mate Fernando Alonso can expect from the grand prix.

"I don't know, I really don't know. It'll be Fernando and myself battling it out and I don't think we'll be seeing another car until they lap us."