Bellusci was at fault as the promotion contenders scored their first goal against Leeds after just two minutes, before then himself netting a bizarre own goal to double Boro's lead.
And Whelan branded the Italian's defending 'shambolic,' stating that he is not good enough to play for United - nor is his ability suited even to the Championship as a whole.
Whelan told the BBC: "It's been shocking defending from the word go. He's been shambolic and I personally don't think he should be on the pitch.
"He shouldn't be playing for Leeds United. I don't think he's good enough. I don't trust him as a player, it's as simple as that.
"He doesn't have the right skill to play for this football club and maybe play in this division."
Considering some of the displays Bellusci has produced during his time at Elland Road - notably at the same Riverside Stadium last year - Whelan's criticism is a little surprising in terms of how frank it is.
The 26-year-old was a member of the 'injured six' last season, of course, which may well make it easier for a Leeds fan favourite like Whelan to lay into him.
Against Middlesbrough this time around, meanwhile, Bellusci was dreadful.
But it's easy to forget some of the times the Italian has stepped it up in defence and won Leeds points with some of his last-ditch tackles and goal-line clearances.