"We are still discussing how much time he (Ajmal) can be away as we now have a scheduled series in Sri Lanka," Pakistan Cricket Board chief operating officer Subhan Ahmed told AFP.
PCB finalised a two-Test and three one-day match series in Sri Lanka, which is likely to interrupt Ajmal's stint with Worcestershire for whom he also played in 2011.
The series was only finalised on the sidelines of an International Cricket Council meeting in Dubai last week.
"It's hugely disappointing," Worcestershire chief executive David Leatherdale was quoted as saying by BBC.
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"You have to get the PCB no objection certificate (NOC) before he is physically available to play."
"You are probably only talking about a few days, but we are in the hands of the PCB, who control his commitments. It's disappointing not to have him here when we had originally hoped."
Worcestershire have also signed New Zealand paceman Mitchell McClenaghan who was due to replace Ajmal for a six-week period in July and August, when the spinner was due to feature in the Caribbean Premier League.