The Belgian was once a highly-rated protege of the beleaguered British team, but he is being replaced by new McLaren rookie Lando Norris for 2019.
"Although I'm very much looking to the future since I confirmed I won't be racing for McLaren next season, I'm also 100% determined to give everything for the remaining races this season," Vandoorne said.
"Both the team and I are pushing very hard to get the best results we can with what we have."
Not normally a controversial figure, Vandoorne has complained about the McLaren car recently, and especially its poor reliability, but even team boss Zak Brown admits that the 2018 machine is not good.
"We continue to push, but unfortunately we have built an extremely poor car that does not respond to changes," he is quoted as saying by El Mundo Deportivo.
"Other teams developed better than us while we seem to have regressed. But we will not give up because we are identifying the problems we have and trying to solve them.
"2019 must be an intermediate step but we probably will not have our full technical capacity until the 2020 car arrives."
McLaren are sixth in the team rankings heading into this weekend's Singapore Grand Prix.