Barca face AC Milan at home this week, having lost the first leg of their last-16 tie at the San Siro 2-0.
Platini believes that anyone can win the competition and also praises his former side Juventus for using homegrown players.
"I've followed Juve for years, they are strong and I like their national identity," Platini told La Gazzetta dello Sport. "Sometimes they are playing with nine Italians. In the Champions League, it will be wide open if Barcelona exit.
"It may even happen that Milan sold [Zlatan] Ibrahimovic and Thiago Silva and are without [Mario] Balotelli, but can beat Barca. It will not be easy to recover the 2-0 loss, even for them."
The match between Barcelona and Milan takes place on Tuesday at 7.45pm.