Fettis says he feels ready for the step up from academy coaching.
He said: “I think the stature of the club. Whenever I've been here with Manchester United's academy they've always been good footballing people.
“It's a really good football club and obviously the manager that has come in has done really well wherever he has been previously.
“Like me, he's a good and honest footballing person, as are all of his staff. It was a big wrench to leave Manchester United after so long but I had ambitions to want to push myself a little bit further so it was a no-brainer really in some respects."