Arsène Wenger says it is important that Ryo stays fit for a consistent period of time.
The Japanese winger picked up a rib injury on the Asia Tour 2013 but could return to full training next week.
Ryo was sidelined for the majority of his loan spell at Wigan Athletic last season and Wenger is ruling out a temporary move for the time being.
“He should come back into full training next week, and at the moment we are not on the way to give more players out,” the boss said.
“Today if you want to exist at the top level, you need to be consistently fit. That is the next step for Ryo, to be every day in training and show how good he is.
“Usually the body stabilises around 21 and adapts to the sport or not, so it is a vital age for him now.”Copyright 2016 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source