The LionsXII goalkeeper suffered a groin injury and will miss the East Asia friendlies and the Merdeka Cup
Izwan is also expected to be out of the Lions' match against Hong Kong on September 10 and has been ruled 'unlikely' to join the U23 side at the Merdeka Cup commencing this weekend.
The LionsXII goalkeeper has been Singapore's first choice goalkeeper since breaking onto the international scene two years ago.
Syazwan Buhari, Neezam Aziz, both of Courts Young Lions are the remaining goalkeepers in the Merdeka Cup squad.
Hassan Sunny is meanwhile expected to play in the China and Hong Kong friendlies with Fadhil Salim deputising.