"He is one of the players that I would have loved to hang on to," admitted the Frenchman on arsenal.com.
"If you take the players in the Premier League who have been educated here there are plenty of them. Steve Sidwell, David Bentley, Fabrice Muamba, Matthew Upson... but at some stage if you don't play them you have to let them go.
"What is important is that they make a career. Upson has made a fantastic career and I knew he was at the age where I had to give it to him or let him go.
"I felt he had, for a very tall guy, quick feet, good pace, a good left foot, a good long ball and he was good in the air. For a centre back that is not bad. He was good on the ball and that is why I am not surprised he has made a good career."