P20 in all three practices and again in qualifying, the McLaren driver had hoped for some improvement in Sunday’s 44-lap grand prix.
Vandoorne told Autosport: “It’s difficult to get a worse weekend.
“We’ve seen the performance we have is very far away from being good.
“There’s not really an explanation.
“The reality is we haven’t progressed since the start of the year, we haven’t progressed at all compared to the others.”
This was not the first time that Vandoorne gave voice to his frustrations at Spa.
Following Saturday’s qualifying, which also saw Fernando Alonso drop out in Q1, Vandoorne told the official F1 website: “Nothing has gone right. In the end the performance is not really surprising.
“We have been struggling all weekend. As a team we have not really done well enough.
“We knew these couple of races we’d struggle a bit more, especially the high efficiency circuits, they seem to hurt us really badly.”