The Nigerian international made one appearance for City, and scored, in the 2 - 2 draw at Chasetown this week.
Dave Jones explained why Oruma is leaving.
"It would have taken a few weeks to get Wilson fit and we told him that," said the City manager.
"He has an offer from another club abroad and needed an answer.
"We couldn't give him that until he was fit.
"We shook hands, he has left Cardiff City and we wish him all the best.
"The kid can play. He has a silky touch on the ball - and just look at the goal he scored. It was an outstanding strike.
"He's been African player of the year twice and it was clear he has genuine quality.
"But he also needs to get fit and we could not give him an answer until then."