McGuigan, who has worked with world champions like Chris Billam-Smith and Lawrence Okolie, didn't hold back when talking about Scott. He questioned how Scott still has a job after what he called "abysmal" work with Wilder.
"I don't know how he's got a job after the abysmal stuff he's done with Deontay Wilder. He's just a guy that talks a load of s**t and all of the s**t he talks never comes to truth."
McGuigan's comments came after Scott called the upcoming fight between Chris Billam-Smith and Gilberto 'Zurdo' Ramirez a "mismatch skill-wise". The fight is set to take place tonight in Saudi Arabia.
The criticism didn't stop there. McGuigan also took aim at Scott's training approach with Wilder, a former WBC heavyweight champion known for his powerful punches.
"He said Deontay Wilder is going to be so much more developed and skilled and he got him shooting to the body with the jab and not using his best attributes and setting up other shots other than his right hand."
McGuigan argued that Scott failed to use Wilder's strengths effectively. He pointed out that Wilder's best shots are his one-two combination and his snapping jab, but these weren't utilized in recent fights.
"But let's be real it's his best shot and his one-two and also snapping that jab out, and he never did any of that in any of the fights. That guy [Scott], he hasn't trained anybody to win any fight of merit."
Wilder's recent performances have been mixed. He lost two fights in his trilogy against Tyson Fury, then knocked out Robert Helenius in one round. However, he lost to Joseph Parker by decision and was knocked out by Zhilei Zhang in June.
The former champion is currently sidelined with a serious arm injury. Fans are waiting to see if and when he'll return to the ring.
McGuigan's full comments were shared by Boxing News on Twitter.