Arsenal lost their final group game 3-1 in the Greek capital Athens, though they won their group anyway.
“It was a fantastic experience they realise what intensity that you need at this level and some young players have shown good things,” he told reporters.
“But there was a bit of lack of experience and maturity in midfield where you need to hold the ball better when we were under pressure.
“We had the early chances, but Olympiakos played a very committed game and made a good battle.”
