Tired after the hectic Indian Badminton League (IBL), Saina decided to take rest but Kashyap was forced to pull out at the last moment as he could not recover from his ankle injury, which he suffered during the IBL.
"I'm not playing the Japan Open as I could not recover from the ankle injury I had suffered during the IBL," Kashyap told PTI.
Sindhu, seeded eighth, will take on two qualifiers in the first two rounds and is likely to make it to the last eight stage without much ado.
In the quarterfinals, the 18-year-old from Hyderabad, in all probability, would face World No.1 and Olympic champion Li Xuerui of China.
A year ago, Sindhu had defeated the Chinese during the 2012 China Masters in Changzhou but Xuerui will always prove to be a very tough customer to get across, considering her exploits at the world stage.