The Rossoneri are keen to capture the signature of Fiorentina's star man but the club's CEO has insisted someone will have to leave to balance the books
Robinho has been linked with a return to Brazil to play for Santos but the transfer has stalled because Milan's asking price is too high for the 29-year-old.
Galliani is not sure whether the forward will be at the club come the start of the season but, if he does depart San Siro, the Rossoneri chief says highly-rated Fiorentina man Ljajic, 21, could be part of their contingency plans.
"If Robinho does leave, there are several candidates to replace him, including Ljajic," he told reporters.
"He is a Fiorentina player and I'm not sure they will want to sell. We are sure, however, we have a great team. Again, if someone leaves, someone will be signed, but otherwise we're okay."
With the Brazilian transfer market closing soon, Milan's CEO knows time is running out to do a deal which would see Robinho leave the club for his homeland.
He added: "We are in discussions, but we only have a week to sort something - the Brazilian market closes on 15 July."
Meanwhile, Santos vice-president Odilio Rodriguez says negotiations are still taking place between Milan and his club over the transfer of the former Manchester City and Real Madrid forward.
Milan's asking price has dropped to 8 million euros from 10 million but no deal has been reached yet.
"The operation is still difficult," he told Globo Esporte. "We need to analyze the total volume of money involved in this operation. But we are still discussing."