The Italian giants have suffered a blow with defenders Mattia De Sciglio, Ignazio Abate and Matias Silvestre all sidelined through injuries.
"When we get injuries, we are unlucky because we tend to get them not only in the same line but in the same positions," Galliani said on AC Milan's official website, www.acmilan.com. "Abate and De Sciglio are the full-backs of the national team but we are able to overcome this setback.
"We have to make sure we do not lose confidence.
"(Cristian) Zaccardo and even (Andrea) Poli can play in that position."
De Sciglio is expected to be out for at least two months as he will undergo knee surgery in the coming days to repair a damaged meniscus.
The latest major setback is Abate, who will undergo further tests in 10 days' time after sustaining a muscle strain against Bulgaria last week.
Silvestre, meanwhile, is undergoing treatment for a meniscus problem while experienced centre back Daniele Bonera is recovering from a fractured kneecap.
Milan are seventh in Serie A and travel to Turin to face Torino on Saturday.