The Japan midfielder has been held back by Emery so far this season - to the reported frustration of parent club Real Madrid.
But Emery told AS: "Kubo is a great kid, he wants to grow up and he wants to do it. He is aware that he has a challenge to overcome, that of being the first Japanese player to reach the top level, and there are a lot of people who want that to be the case and want to speed up the process.
"But this acceleration is not good, he must adapt and develop to be competitive in all options and positions. He can play in three positions, the right winger position is the one that suits him best, but there is a lot of competition. In the centre he works to improve and on the left he has to grow more so we are in this process. I understand the noise from the media, he's a star off the pitch, but he has to be one on the pitch.
"Our obligation is to do it in the best possible way and to take care of him so that he can achieve this goal. I have not told any player that he is guaranteed to play, or that we will be champions by counting on him, it is something that I would not do. To achieve a goal, it's everyone's business, the whole team, not a single player as good as he is."