The Dutchman joined in the final days of the transfer session from Manchester City, but has so far been unable to turn their campaign around.
"I had a similar period at Hamburg when I was playing there," he told onsoranje.nl while on international duty.
"Italians are emotive and passionate, but we have to stay calm. How long will it take to get out of this crisis? Don't forget 12 players left and two of them were the best in the squad.
"I hope it won't take too long, but we must be realistic, even if naturally we remain Milan."