Xabi was axed this week after Saturday's Spanish Super Cup final loss to Barcelona.
It's since been claimed never won over the Real dressing room, though Bellingham denies he was actively working against his former coach.
He posted to social media: "Until now l've let far too many of these slide, always hoping the truth will come to light in its own time.
"But honestly... What a load of s***.
"Truly feel sorry for the people that hang onto the every word of these clowns and their 'sources'.
"Do not believe everything you read, every now and then these lot need to be held accountable for spreading this kind of damaging misinformation for clicks and added controversy."
Caretaker coach Alvaro Arbeloa, who has stepped up from his Castilla role, took charge of training for the first time yesterday.