Former coach has revealed that used to 'sneak' away to visit his birthplace, London, during his struggles at the club. Sancho has thrived since arriving at in the summer, and McCarthy believes how much closer he is to home is contributing to his positive start.
The 24-year-old called time on his woeful United career on deadline day, joining Chelsea on an initial season-long loan with an obligation to buy worth £25million.
He has registered an assist in each of his first three games for the club - wins against , and .
And McCarthy, who also left United in the summer, claims that Sancho spent lots of time in London during his time at the club due to homesickness, an issue he has now resolved.
"He's closer to home because he did sneak out to come to London quite a lot," McCarthy told the podcast.
"So probably the fact that he was missing home, and, just wanted to be a bit closer to to family and friends and his culture.
"The London culture is quite strong, so I think Jadon maybe wanted more of that. So that's why he kept on. He was in London quite a lot.
"Now he is closer to home, so hopefully he can find that peace, he can find that bit of magic that that he found when he went to Dortmund, and he gets the love that he deserves from the coaching staff, the players.
"I think he will turn out to be a special player again. Because I think every single one that knows Sancho would want him to be at that level because it's good for world football."
McCarthy returned to United for two years as Ten Hag's attacking coach before Ineos didn't extend his contract.
The South African will have been at the centre of Sancho and Ten Hag's public row last season, which ignited the spark that led to his switch to Stamford Bridge.
He has shared his regret over how the situation transpired, claiming a lack of communication between the two parties was the primary culprit.
McCarthy said: "Just a bit of communication problems, really, because Sanch is a very quiet guy. No one knows literally anything about Jadon.
"Jadon comes in, he does his job, he does his he does his work, and then it's just like, very quiet. [He's] a great boy, great character, fantastic footballer, unbelievable the things that he can do.
"For me, it was a real shame that it didn't work out for Jadon at United because I thought he was the type of player that would flourish in a United shirt.
"But unfortunately, I think lack of communication and understanding was part of the downside that didn't end up working with Sanch."
