The Italian champions will head into the second leg at Camp Nou on Tuesday 2-0 ahead from the first leg played at the San Siro last month.
"We have so much to lose but also so much to win," he told UEFA.com. "We are in a positive situation, but in my opinion this tie still stands at 50-50.
"Last year we beat Arsenal 4-0 yet we were still close to being knocked out. We have players with a lot of experience, but I also know it won't be easy for our younger players, although the experience will do them good.
"Honestly, I don't think what happened against Arsenal will happen tomorrow. We don't see the match any other way than to play it with a knife held with our teeth."