Two seasons as a loanee under Bielsa at Leeds United have, without a shadow of a doubt, made Harrison a better player – the evidence for the argument is overwhelming.
He has improved almost every single quantifiable skill or contribution that he can bring to the table for his loan club and his five goals and seven assists tell so little of the story.
The upward trajectory of his statistics and metrics goes a long way towards explaining why, with nine games still remaining in the coronavirus pandemic hit season, Harrison has already played 339 minutes more first team football for Leeds United this season than last.
His first touch, his speed, trickery, willingness to run for 90-plus minutes and an improved quality of delivery have made him a nightmare for opposition defenders in the Championship.
All in all, he has had the kind of season that suggests, strongly, his future will contain a lot more than second-tier football.
For Manchester City, it is the dream scenario for a player out on loan.
They know that Leeds United will either exercise their option to make the deal permanent and furnish City with cash – a bargainous £8m – or they will retrieve a very saleable asset worth a lot more than that.
They might even, if Leeds for some reason decide not to act, welcome him back as a player able to play a part in Pep Guardiola’s plans.
Harrison counts himself fortunate to have experienced life under both Bielsa and Guardiola, a man who once travelled 5,000 miles just to meet the Argentine.
“I have a lot of admiration for both managers,” said Harrison.
“They both have a very good reputation around the world and I’ve been lucky enough to work with both of them, even though with Pep it was only for a short amount of time.”
The two years he has spent in Bielsa’s intense Thorp Arch regime have given Harrison a platform that he believes has prepared him for almost any eventuality, even a return to the Etihad Stadium.
“For the last two years working with Marcelo I’ve learnt a lot and develop different parts of my game and improved,” he said.
“Working with him has already prepared me for almost anything going forward.
“It’s an exciting opportunity if I was to go back to Man City and work again with Pep Guardiola.
“What I’ve learnt with Marcelo I can take anywhere and if it is back there, it’s another great opportunity for me.
“I’ve learnt a lot over the last two years and I can take it wherever it may take me.”