Borussia Dortmund coach Jurgen Klopp says returning Manchester United boss Sir Alex Ferguson is a one-off.

Klopp admits he regrets not visiting United to see Ferguson in action.

He told The Sun: "My whole life as an adult Alex Ferguson was coach of Manchester United. I only know this club with him as a coach. It's unbelievable what he's done. I never had the time, nor the possibility to go to Manchester United and watch training. I worked as a coach and never had the time to go see what others are doing.

"It's one of the biggest stories in the history of football. I don't think anyone will ever do that again. He's a great manager and really it's not possible to do twice what he did there. Or something similar.

"I don't know if I would like to do it myself."