Chelsea signed the 20-year-old US international in a £58.7 million (A$105m) deal from Borussia Dortmund in January, beating several clubs, including Manchester United, to his signature.
But Pulisic's former manager at sixth tier club Brackley Town, where the midfielder spent a season as a youngster in 2005, Robin Walker, claimed United were never really in the running.
Walker revealed that Mourinho's reluctance to give young players a chance was a major sticking point with Pulisic's father.
"He wouldn’t go to Manchester United because of Jose Mourinho," Walker told UK paper, The Telegraph.
"His father couldn’t stand Mourinho, because he didn’t promote young players. It was at that point I asked: ‘What about London? That’s where it’s at.’
"I was trying to sell the city. His agent agreed, saying: ‘When you make these decisions, it’s all about investment and property.’ I was delighted that he did sign [for Chelsea].”
Mourinho was eventually sacked by United in December and replaced by Ole Gunnar Solskjaer.
Pulisic made his debut in Chelsea's 4-0 loss to United on the opening day of the Premier League season after coming on as a second half substitute.
He also had a goal disallowed in the Chelsea's UEFA Super Cup dramatic penalty shootout win over Liverpool.
