Ajmal, 37, was suspended in September and has been receiving the help of former Pakistan spinner Saqlain Mushtaq to correct his action.
The PCB said he has shown "significant improvement".
"The PCB has decided to extend Saeed Ajmal's remedial work under Saqlain by another 15 days," the PCB said.
"After further remedial work in the next fortnight, Ajmal shall be sent over to an high-quality lab in England for testing to ascertain the exact degree of improvement in the ace off-spinner's action," the body added.
Under ICC rules, bowlers are permitted to straighten their bowling arm up to 15 degrees, which has been established as the point at which any straightening will become visible to the naked eye.
Ajmal will only be allowed to return to action after an assessment finds the action within the allowed limits. Saqlain earlier this month said he wanted Ajmal to return before next year's World Cup in Australia and New Zealand.
Bangladesh's paceman Al-Amin Hossain was reported last month and is in danger of also being suspended.
