Ian Bennett was drafted in as a replacement for the Belgian custodian, 33, who admits to feeling 'disillusioned'.
"It was a complete surprise to be on the bench," confessed Vaesen.
"We may have lost our last four, but they were against clubs like Manchester United and Arsenal, and that says it all.
"I still felt I was doing a good job, so that's why I find the decision so spiteful. I'm thoroughly disillusioned.
"Steve Bruce said he wanted to take me out of the firing line, to give me a few weeks' rest in order to regain my fitness.
"It is a real shame that my record has gone. I won't panic, though, as I know that in top-level football these days clubs operate a rotation system."
Vaesen feels that Bennett's inclusion was more of an off-the-field decision aimed at persuading the number two keeper that he has a future at St Andrews.
"But my impression is that I have been left out for non-footballing reasons," added the former Huddersfield Town shot-stopper.
"Ian Bennett will soon be out of contract, and maybe the club wants to see whether he deserves to be given an extension."
