While the Woking-based squad has been unable to match the pace of the leading outfits, Button insists McLaren took a step forward in performance in the Hungarian Grand Prix last month.
While he finished in seventh position at the Hungaroring, the Briton is optimistic Spa will suit his car even better.
"Seventh doesn't look exciting, last race we were fighting for a fifth, but I still think we've made a step forward, because the Mercedes looked quicker compared to the opposition," Button said of his Hungarian Grand Prix result.
"I think we've done a good job, and I think we'll really show that at Spa.
"It's a different type of circuit, and a circuit that should suit what we put on the car for this race.
"It [Hungary] was probably our best race of the year. That's not saying much, but it's been a tough season.
"There is progress there, and I think we should be happy."
Button, who is yet to finish on the podium this year, believes the Belgian track's layout will allow his team to really show it has closed the gap to the frontrunners.
"It's got to the point of the season where there is a gap between the top teams and the slower teams, and we are in that gap," he added.
"I think the next race you'll see us a lot closer to the top teams, and fighting with them. I'm looking forward to Spa already."
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