Striker Cristiano Ronaldo – the world’s second best player behind Lionel Messi – will be back at Old Trafford for the first time since he left Man U for Real when they play the knock out fixture.

Arsenal have copped a toughie in last season’s beaten finalists Bayern Munich, but the reality is there are no easy games come this stage of the competition.

Scotland’s Celtic face Italian champions Juventus, while Barcelona meet AC Milan, Borussia Dortmund play Shakhtar Donetsk and Valencia host Paris St Germain. FC Porto will welcome Spain’s Malaga while Galatasaray clash with suprise packets Schalke.

Man U club secretary John Alexander told Sky Sports News: “Out of several standout ties, I think this is the one.

“It’s the tie that everyone wanted to see – but that nobody wanted to see, they wanted to save it for later in the competition.

He pointed out that Man U’s one victory over Real Madrid was in the equivalent of the Champions League … in 1968.

Ryan Giggs and Rio Ferdinand were playing in 2003 when the teams last met, with Real finishing 6-5 on aggregate.

Cristiano Ronaldo last played for United in the Champions League final where they fell to Barcelona.

He then took a world record £80million transfer fee to move to Madrid.

All group winners will play the second leg of their two-match ties at home.

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