The deteriorating situation in Greece—including long lines and a 60 euro ($67) limit at ATMs—could get much worse if voters there refuse to accept creditor-imposed reforms in a referendum this coming Sunday, said billionaire Wilbur Ross, who has a large interest in the country.

"Once there's social unrest, which there will be before too long if this thing continues, no tourist is going to want to go to [Greece]," Ross told CNBC's "Squawk Box" on Monday. "If the Greek people understand how limited those concessions that are requested are, and contemplate going into the abyss on other side, they're never going to pick the abyss."