The 26-year-old right-back conceded an 87th-minute penalty which Tjaronn Chery converted as the Londoners denied Steve Evans's side - who went ahead through Chris Wood - three points at Elland Road.
The Italian was subjected to widespread booing by the Whites supporters following the error - his second in a matter of days after a ridiculous overhead kick inside his own box ultimately led to Rotherham United snatching a last-minute winner in their 2-1 victory on Saturday.
However, Abbott feels that the reception he received was harsh, noting that Bellusci has been "pretty decent" all season long for Leeds.
Asked if the jeers were justified, Abbott said to TV Yorkshire: "No, not to boo him as loudly and as wildly as that. Over the season he's been pretty decent.
"He's been consistent. He wasn't great tonight - it's the poorest game he's had, it wasn't just an individual error, he was poor all the way through and he didn't look quite where he needed to be.
"He looked all at sea. Sometimes when that happens you make those mistakes he has done for the goal, and he'll get some criticism, but I thought the booing was a little bit harsh."
The result ensures that Leeds are not winless in three, having lost at Rotherham at the weekend as they failed to bounce back from the demoralising 4-1 defeat by Huddersfield Town the previous week.
On Saturday, they face Championship leaders Burnley at Turf Moor.