MANCHESTER, England, Aug 15 (Reuters) - Manchester United's ( MANU ) newly acquired centre-back Matthijs de Ligt said his long playing partnership with Noussair Mazraoui will be a big boost to United's back line, an area that was decimated last season by injuries.

The defenders signed contracts on Tuesday from Bayern Munich making United their third team together, and they could both feature in the squad's season opener on Friday against Fulham at Old Trafford.

"What can I tell you about Nous? He is an amazing guy, an amazing player," De Ligt said in an interview with the team's in-house media.

"I've known him already for a long time, I think around 10 years now. There's a reason we always come together, like before in Ajax, then at Bayern Munich, now at Manchester United ( MANU )," the 25-year-old Dutch defender added.

"I think it is a special relationship and I'm really happy and glad that he's also going to be here, and I think we can help each other a lot."

De Ligt, who signed a deal until 2029, and Mazraoui, whose contract runs until 2028, have played more than 100 games together at Bayern and Ajax.

They also know Erik ten Hag well, having both played for the United boss when he was Ajax manager.

"He has played a big part (in my development), to be fair. He was the first trainer who made me captain, I was 18 years old and he just gave me so much confidence," De Ligt said of Ten Hag, who made him the youngest captain in Ajax's history.

"He told me right from the start: 'You are an example for the team, and I want you to be captain.' Just the confidence he gave me at that time, at that age, was really special."

United have largely rebuilt their back line from last season, which is part of what drew De Ligt to the team, he said.

"I actually really like the project," he said. "It's always nice to go somewhere and to feel that you're part of a new project, to feel that you're part of something new."

"Hopefully myself, and the other players that are coming this summer, can give a great piece to the next history of Manchester United ( MANU ) and to get the club back to where it belongs: on top."