The 25-year-old is on loan for the season from Juventus and reports in Italy have suggested the deal could soon be cut short to avoid triggering a permanent move.
But Bilic insisted he could still come good – just like Dennis Bergkamp did at Arsenal.
He said: “He is definitely a good player who came from a big club to a new country. New players need time.
“If we go back and think about Bergkamp, who needed – I don’t know – a year? – the problem now is, and it is quite common with even the best players from abroad, they need time.
“Plus he wasn’t a regular there and didn’t have match fitness.”