Despite consistent excellence in training, the 18-year-old England winger was used sparingly by coach Maurizio Sarri, starting just four Premier League matches.
"We were in the dressing room last season and the players were saying 'how is he not playing?'," Green told BBC Radio 5 Live.
"He was going out in training and tearing some of the best defenders in the world apart. He was consistently the best in training.
"It was to the point where some of the best players in the world were standing there applauding what he was doing."