"All we were missing was the goal," he said of the Old Trafford loss. "They scored four minutes into each half and when that happens it does knock you down.
"We continued playing, hit the woodwork twice and I had another two chances go so close. We played with confidence and character, but it was not enough."
The Nerazzurri had said the Champions League was their main target for this season, but go out in the second round for the third year running.
"It's a shame, as I really wanted to win this trophy and it was my primary objective for the campaign.
"I gave my all, but it wasn't enough. In the first half I was a little isolated upfront, but the tactics worked.
"We changed a few things after the break and had more chances, but could not find a way through. I am very disappointed, but we must look ahead and win the Scudetto."