Barca respect United greatly and know they’re the commercial trailblazers to look up to off the field. Barca expect to win and with Atletico and Real Madrid out of the competition, dominated by the latter in the last half-decade, the Catalans have their eyes on winning the treble topped by lifting the European Cup in Spain’s capital in June.

Absolutely nothing, bar beating Real Madrid in the capital, could be sweeter during these politically charged times of tension between Catalonia and the rest of Spain.

Barca knocked Madrid out of the Copa del Rey and left them behind in the league, but what of the United team they’ll meet, first at Old Trafford before the return at Camp Nou?

Consecutive defeats at Arsenal and Wolves have popped the bubble of invincibility which surrounded United since Ole Gunnar Solskjaer took over. Saturday’s defeat at Molineux was the worst performance under the Norwegian and it came in the competition United had the best chance of winning.

It’ll be fascinating to see if they have the mental strength to come back from it for they have a very tough April, with those Barca games and matches against City, Chelsea and Wolves away again.

Yet, even Solskjaer’s 1999 treble winners needed to come back from a terrible December 1998 when they lost to Spurs in the League Cup, drew four in the League in a row before losing at home to Middlesbrough. They got their break and a surge in belief after a Solskjaer last-minute winner against Liverpool in the FA Cup fourth round.

United’s side of ’99 were superior to the 2019 version, but positives could come from the recent defeats, just as they could if Barca hammer United like they destroyed Lyon 5-1 last week after drawing the first leg or Sevilla 6-1 in the second leg of the Copa del Rey after losing the first leg.

It would show that this United side still needs serious improvement and a direction lacking since Alex Ferguson stepped down. Normally, I’d say investment rather than improvement but United have spent big with patchy results.

Alexis Sanchez, their best paid player, has been a significant disappointment.

Domestically, Liverpool and Manchester City are better than United, but there are reasons for optimism at Old Trafford. Solskjaer and his team are one, the belief players have shown in him another, but that’s not all.

Unlike fellow Champions League quarter-finalists Ajax, who are resigned to losing their best players each year, United are in a position to strengthen this summer. They just need to be smarter over the players they sign.

United are still looking to appoint a sporting director to work alongside the first team manager – most likely Solskjaer – and Ed Woodward. It’s a vital role since recruitment is the crucial area where United have underperformed.

United need a brilliant right back, they need to sort out the centre of defence and they need another forward player if Sanchez is to continue to underwhelm. Their central midfield was also outclassed at Old Trafford against Juventus and PSG.

Talk of a sporting director quietens when the team wins, then increases when it doesn’t but after the high levels of recent failure and the stronger financial power of domestic rivals, this is a key appointment.

Sanchez, Memphis Depay, Morgan Schneiderlin, Henrikh Mkhitaryan, Bastian Schweinsteiger, and Radamel Falcao all arrived at Old Trafford either on vast wages, a huge transfer fee or both. All underwhelmed.

United shouldn’t become the club that every top player flirts with when they’re unhappy or wants a bigger contract, as Sergio Ramos and Cristiano Ronaldo did. With a savvy, connected, sporting director, United should be ahead of the queues to sign the next Bernardo Silva rather than react to the whims of a star.

Given the past failures, United should be wary when players like Antoine Griezmann makes himself available, as he has done this weekend.

Griezmann already earns more than any United player and his buyout clause drops to €120 million (£103 million, US$136.1 million) this summer. He’s hugely talented and United tried to sign him in 2015, but what was right then might not be right now. Is just going for “big names” who want the most money the right way forward?

Some of United’s greatest signings weren’t big names while others were emerging rather than established talents. Roy Keane was the best young midfielder in the league when he arrived in 1993, Gary Pallister the best young defender in 1989. Antonio Valencia came from Wigan Athletic. Players joked that they thought the baby-faced Solskjaer was a teenaged “meet the team” competition winner when he first arrived, but good scouting and trusted contacts alerted Ferguson to him, rather than an agent wanting to cut a deal.

Agents representing stars are vital in 2019, but all United’s top five appearance makers in their entire history came through the youth ranks. Home-grown youth, as Ajax have found, really can lead the way and bring unmatched excitement. After being under-resourced, United’s youth system is working once again and Solskjaer is a manager who will play youngsters too.

That’s another reason for optimism as United try to get back to the same levels as the best who, partly because of various self-inflicted wounds, have left them behind.