"There is no restriction or reservations from us or the ICC. The fact is that the national selectors can consider them for selection but first they have to show their form and fitness at a consistent level in domestic cricket," Khan said.
His remarks came after Asif and Butt said they were contemplating writing a letter to the ICC to confirm whether the world body had any reservations on them playing for Pakistan again.
Butt, Asif and Mohammad Aamir were found guilty of spot-fixing during the tour of England in late 2010 and sentenced to a minimum of five-years ban.
The ban expired last September and while the PCB permitted left-arm pacer Aamir to make a comeback to the national side, it has not had a clear policy on Butt and Asif.
But the PCB chief finally made it clear they can also be considered for national selection provided the selectors felt they were required.
"If they can perform consistently at the domestic level in first-class cricket they can be considered by the selectors who have not been given any instructions not to select them," Khan insisted.
He also pointed out that the case of Aamir was different from those of Butt and Asif as the former was shown leniency and given some relaxation by the ICC and allowed to resume playing domestic cricket before his ban expired.
"But if Butt and Asif do well and fulfil all ICC anti-corruption requirements there is no bar on them playing international cricket again."