Manchester United manager Ole Gunnar Solskjaer said his side must "aspire to Barcelona's level" after their Champions League quarter-final defeat.
Lionel Messi inspired Barca to a 3-0 win in Tuesday's second leg at the Nou Camp, sealing a 4-0 aggregate victory.
"If we want to get back to Manchester United's true level, true traditions, we have to challenge Barcelona," said Solskjaer.
"They were a couple of levels above over the two games."
Messi scored two goals in four first-half minutes, with Philippe Coutinho adding a stunning long-range third in the 61st minute.
United struggled to contain their opponents and had just three shots on target over the two legs.
Speaking to BT Sport, Solskjaer added: "Lionel Messi is top quality and he was the difference, of course. At 2-0 straight after, it was game over. Messi showed his quality."
Solskjaer's side face a battle to qualify for next season's Champions League in their remaining five Premier League games.
They are sixth in the table, two points behind fourth-placed Arsenal, and travel to Everton on Sunday before hosting title-chasing Manchester City on Wednesday, 24 April.
"We want to play these games again next year, so we have a massive week coming up," Solskjaer added.
"There is no point dwelling on what could have been. We have to focus on that week."
'The next few years will be massive for us'
United have not reached the last four of the Champions League since 2011 and were competing in the quarter-finals for the first time in five years.
Solskjaer said he knows there is "work to be done".
"We have said all along that this isn't going to change tonight. The next few years will be massive for us to get to the level of Barcelona," Solskjaer said.
"We have got good players and, at the moment, we really have done well to get to the quarters and to get in the challenge for the top four.
"We have got a rebuilding job but that starts with the coaches and the players and one or two additions to the squad will happen in the summer."
We have shown who we are - Messi
Barcelona had lost three Champions League quarter-finals in a row, including their dramatic collapse against Roma last year, but are now into the semi-finals for the first time since they won the competition in 2015.
Captain Messi said they have "shown who we are" with the performance.
"We put on a spectacle and played a great game," the Argentine said.
"But we came out cold and looked nervous in the first five minutes. It was a bit weird until we regained control of the game and we scored the first goal.
"We cannot come out like that in a Champions League match because we have the experience of Rome last season and it could [have] made qualifying difficult.
"Five bad minutes can knock you out."