Barcelona assistant manager Jordi Roura admits they had more problems than expected at San Siro, but “we fully believe we can turn this around.”
Milan soaked up pressure for an hour before striking to win 2-0  with Kevin-Prince Boateng and Sulley Ali Muntari.
“We struggled to find depth and to reach their goal,” said Roura, standing in for the ill Tito Vilanova.
“Obviously this wasn't our best game. Although we had problems I think that the result is excessive.
“They found a couple of opportunities and scored from them which now makes things tricky for us.
“We all know how difficult it is in this stadium. They have defended with everything behind the ball, very orderly. We struggled to find depth.”
The second leg at the Camp Nou is in a fortnight and Barcelona have to win by three clear goals to qualify for the quarter-final.
“The comeback will be difficult, it is two goals, but we have confidence, for our players, for our stadium. It will be a different story in the second leg. We fully believe we can turn this around.”