Ole Gunnar Solskjaer has admitted Manchester United need a huge overhaul in order to return to Europe's elite ffter their slim hopes of another famous Champions League revival were killed off by Lionel Messi and rampant Barcelona.
Although United made a bright start to their quarter-final second leg at the Nou Camp, with Marcus Rashford hitting the crossbar early on, they were soon outclassed by Barca as the hosts eased to a 3-0 win on Tuesday night for a dominant 4-0 aggregate victory.
"We were fighting against a great team and we know there's work to be done but I've said all along this isn't going to change overnight," Solskjaer told a news conference.
"The next few years are going to be massive to get to the level that Barcelona and other teams are at."
Solskjaer has restored United's confidence and overseen a vast improvement in results since he succeeded the sacked Jose Mourinho in December, giving them hope of a top-four finish in the Premier League.
He also led them to an historic comeback after a 2-0 first-leg defeat at home to Paris Saint-Germain in the Champions League last 16, going through on away goals with a 3-1 win in the French capital.
Yet the scale of the long-term surgery required was laid bare at the Nou Camp.
Messi pounced on two United errors for his two goals - the second further gifted by a howler from the usually excellent David de Gea.
"We've got good players to work with and at the moment we've done really well to get to the quarters and challenge for top four, but we've got a rebuilding job," Solskjaer said.
"It starts with the coaches and players, and with one or two additions.
"We're on with the job and have spoken to the players we need to get the best out of each other, create an environment of top class attitude, world class attitude every single day."
Philippe Coutinho netted Barca's third when he was left with plenty of space and time to curl a shot into the top corner.
"We did well to get here but we could see the difference between the two teams," Solskjaer said.