The veteran's guile and industry in midfield helped Milan secure a 2-0 advantage three weeks ago, but, with a place in the quarterfinals up for grabs, the 35-year-old says the tie is still very much open.
"We have much to lose but a lot to gain. We are in a positive situation, though, in my opinion this tie is still rated at 50-50," Ambrosini told reporters at a press conference.
Ambrosini also identified where the Italian giants pose most threat to Barcelona and insists the team have learned to appreciate the danger of a first-leg advantage after the scare they suffered against Arsenal last season.
"Last year we beat Arsenal 4-0 and we were close to being knocked out in the second leg," Ambrosini said. "Barcelona will take hold of this game like Arsenal did, but our main weapon is the counterattack. We have the grit between our teeth and are ready for any situation."