BARCELONA, Spain -- Ole Gunnar Solskjaer has admitted he faces a rebuilding job at Manchester United that may take years after a humbling Champions League exit to Barcelona.

United were out-classed by the Spanish giants, who eased to a 3-0 win at Camp Nou thanks to two goals from Lionel Messi.

It stretches their wait for the Champions League semifinal to eight years and Solskjaer says he has work to do to get his team back to that level.

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"We know there's work to be done," said Solskjaer.

"I've said all along this isn't going to change overnight and the next few years are going to be massive to get to the level of Barcelona.

"We're on with the job and we've spoken to the players about it as well.

"We need to create an environment of top, world-class attitude every single day. We've got a lot of good players to work with but as I have said, we have a rebuilding job. It started with coaches, players and of course one or two additions in the summer."

Looking to overturn a 1-0 deficit from the first leg, United started well against Barcelona and could have taken the lead after just 24 seconds when Marcus Rashford hit the bar.

But any hope was extinguished when Messi scored twice in four minutes in the first half -- the second squirming under David De Gea's body and into the net.

Ole Gunnar Solskjaer says Manchester United have already started their rebuilding efforts. Getty

"That's unfortunate with goalkeepers, when you make an error it can get highlighted and that'll be remembered," said Solskjaer.

"He made some fantastic saves and his contribution to the team is good but sometimes that happens in football."

Both Rashford and Scott McTominay had early chances as United started on the front foot but after Messi scored with Barcelona's first two shots on target the tie was all but over.

Philippe Coutinho added a stunning third in the second half, curling a shot beyond De Gea from 25 yards.

"We did well to get here and the quality of their finishing was absolutely outstanding," said Solskjaer.

"We started well in the first five minutes and we felt we've got something here and then in four minutes they scored two goals.

"The attitude was right but we were fighting against a good team.

"Messi is an exceptional talent. Him and Cristiano [Ronaldo] have been the best players in the world for the last decade and he showed why we think that and why this team have won so many Champions Leagues.

"If you give him space and time around the goal he'll create and score goals. He's a fantastic player."