Van Dijk's career nearly took a different path, however, as Man City were offered the chance to sign the 28-year-old from Celtic in 2014.
"Did I get in touch with City? Yes," Deila told Goal. "I said you have to take him. They said, 'okay, tell me the best European game he has played and we will watch it'.
"I couldn't tell them what game that was because he hadn't had any real good European games. He was really dominant in Scotland but he got sent off against Inter [Milan] away.
"That was a big test. I think if he had played fantastically in that game, he would have been bought.
"I think Van Dijk was good, but he didn't have that one really, really good game in Europe."
Deila spent two years as Celtic manager and is now in charge of Major League Soccer side New York City FC.