The Catalan giants were thrashed out of the Champions League group-stage last month as they finished third behind Bayern Munich and Inter Milan in Group C.
They have now been demoted to the Europa League and will face Man United in a two-legged affair to make it to the round-of-16 of the competition.
“It’s the most difficult opponent once again. We are looking forward to it. They are a historic side, they have grown a lot since Ten Hag’s arrival, and have great players. It’s the worst draw we could have got,” said Xavi while reacting to the draw on Monday afternoon.