The former Barca forward is due to face his old team on Wednesday and believes a first-leg defeat would destroy Milan's chances of an eighth Champions League title
The Rossoneri welcome Tito Vilanova's side to the San Siro on Wednesday night and Bojan believes a first-leg defeat by Barca would effectively end the tie as a contest.
Speaking to Uefa.com, Bojan said: "We will be playing the best team in the world but have the backing of the San Siro crowd.
"We will have to earn at least a draw to give us hope for the return leg."
The 22-year-old left Camp Nou in 2011 in search of regular football and the striker has revealed he remains in contact with his old team-mates.
He added:"I have been speaking to a few of my former team-mates and I will swap my shirt with [Andrés] Iniesta after the match."