United has been strongly linked with a move for Dortmund and England sensation Sancho, though his club has repeatedly insisted the 20 year-old will not be sold ahead of the 2020-2021 season.

Sancho established himself as one of the hottest properties in European football last term after scoring 17 goals and supplying 16 assists for Bundesliga runner-up Dortmund, prompting links to the likes of Real Madrid, Liverpool and Barcelona.

As United reportedly continues to try to negotiate with Dortmund – which remains unmoved on its £108million (€120m) valuation – former Red Devils winger Olsen said: "It's always difficult because you see somebody and you like what you see and you would like them to play for your team. You have to come up with the money and after that, it's only when it begins because you want them to perform.

"If you can get somebody of that class and they want to come to United, of course you pursue it to the end. I've always tended to watch a lot of German and English football, but when you look at the likes of Bayern Munich and the way they perform, you know it's going to be very hard.

"You have incredible teams at the top of Europe, so you have to have bigger squads. Any player of that calibre that can add something to the squad, of course you look for that."

While a blockbuster deal to bring Sancho to Old Trafford is proving difficult, United is poised to sign star Ajax midfielder Donny van de Beek.

Ole Gunnar Solskjaer is determined to bolster his squad after leading United to a third-placed finish in the Premier League last season and Champions League qualification.

United enjoyed a 14-match unbeaten streak in the league as it secured a spot in the top four, while Solskjaer's side also reached the semi-finals of the Europa League, FA Cup and EFL Cup.

"Overall, it's fantastic for Manchester United but also Ole Gunnar Solskjaer," Olsen, who won the FA Cup during his four years at United, said. "All the flack that he got for a long, long time as you do when you manage United and not doing well. But you go back to [Alex] Ferguson's era, and it takes time to build up and get the players you want, the team playing the way you want. Sadly nowadays, you don't always have the time.

"We know how difficult it is to win anything in any sport around the world. Everybody says yeah we should win, but it is so tough to win anything, even getting into the semi-finals and final. To actually win something is not easy.

"I'm happy to see them play well. They were really getting into top gear at the end of the season. For Solskjaer too, he is a good guy. He is calm and collected and I think he is the right man for sure."

Bruno Fernandes played a key role in United's resurgence after his January arrival from Sporting CP – the Portuguese midfielder scoring eight goals and supplying seven assists in the Premier League.

Fernandes also managed 12 goals across all competitions as United featured in three semi-finals in 2019-2020.

"He has shown, with the way he plays – simple and effective, and just makes things happen. This is what we need. He also has a good engine," former Ajax and Denmark star Olsen said.

"He's settled down some of the younger players too. Daniel James wasn't involved so much at the end of the season but then we look at [Mason] Greenwood. That's what we call exciting players. This is what you want to see."

Doubts over David de Gea's long-term position also emerged during the season, highlighted by his errors in the FA semi-final loss to Chelsea behind closed doors at Wembley amid the coronavirus pandemic.

"I think defensively, they made mistakes at the back. Sometimes it looked a bit like the goalkeeper De Gea and the defenders didn't fully understand each other but that happens in a lot of teams," Olsen said. F"or a long, long time we played structured with a strong defence.

"But suddenly, a part of the season something seems to go a bit – tiredness or playing in front of empty stadiums I don't know but certainly there were some things that could be avoided.

"That happens throughout the season. I think Barcelona are going to look back against Bayern and think it was like they weren't there. For everybody, even though we say thank God they can play and finish the season, but there's so many external things that happen to players with families.

"Not only around themselves but family abroad. It must be a worrying time, like for all of us, for them too. And then have to go and perform and kind of say, let's forget about that even though I think they're happy they can still play because it takes away mentally some of the other things. It must be the biggest nightmare for all of us, but also to go perform in empty stadiums, it makes no sense. We have to kind of allow them to have made a few mistakes given how the world is at the moment."

United finished 33 points behind bitter rival and champion Liverpool last season but Olsen feels the Manchester club – which has not won the league since Alex Ferguson's final campaign in 2012-2013 – can challenge in 2020-21.

"This season, I thought City were going to win the league again because when you look at Pep [Guardiola]'s record. It shows, there's some games and some part of the season that you don't always perform well. Then you have the added pressure of the Champions League, which is really, really important," Olsen added. "For status but money-wise. There's a lot around the Champions League these days and that's where the bigger clubs want to be. All the excitement of playing against the best in Europe.

"I think Manchester United, certainly with Champions League qualification, can test themselves. I think anyone that goes to Old Trafford, it will be hard to win there. If you can go away now, have a settled team, a structure and play how you want to play, then I think they have as much chance as anyone else to win the Premier League and go far in the Champions League for sure."