Manchester United never know when they are beaten and must not be underestimated by Barcelona in the Champions League, says Gerard Pique. Ole Gunnar Solskjaer's side set up the quarter-final tie after producing a stirring comeback against Paris Saint-Germain last month in the last 16. And Pique – who spent four years at the Red Devils before returning to his boyhood club in 2008 – has cautioned against complacency if they do leave England with a first-leg advantage. "I've seen the replay of Manchester United v PSG," he told a media conference. "It's a good example. "You can never leave Manchester United unmarked. You've got to finish off the job. They showed that in the second leg against PSG. "They've got a lot of good young players. The penalty at the end is a big example of what can happen. We know how dangerous United are."