The Gabon striker joined the north London club on deadline day, leaving Borussia Dortmund in awkward circumstances after relations with fans and the board soured.
Earlier this week, Dortmund chief Hans-Joachim Watzke accused Aubameyang of withholding performances at the German club, raising questions over the striker’s attitude.
However, Pulisic has backed him to succeed and praised his character.
"I think you guys know what type of guy he is. He shows that,” the American playmaker told ESPN FC. “But, what I think you guys really don't know is just how nice of a character he is and how much he cares and how hard he works.
“I mean, he brought me along so much as a player and helped me and guided me, and he's been such a great guy. Obviously, we're sad to lose him, but I'm excited to see what he does."
Pulisic has, like most Dortmund stars, been linked with a move to the Premier League and, while he hailed the division as ‘unbelievable’, says he’s committed to the Bundesliga club.
"Of course, the Premier League is an unbelievable league. You never know in football what can happen, so right now, I'm focused with Dortmund, and yeah, that's that."