Chelsea goalkeeper coach Christophe Lollichon says Thibaut Courtois must spend another season away on-loan.
Lollichon says the Belgian, while impressive with Atletico Madrid this term, isn't quite ready to be a No1 for Chelsea.
"He needs more strength to compete in English football. Besides, there are also some other aspects he must work on. But he is still young and has time to work on these things," said Lollichon.