Aftab Gul, one of the lawyers who had been representing Butt, told Reuters the ICC had rejected a 40-page reply filed this week.
“Now the ICC has said that he must file a fresh reply by later today or he could lose his right of defence against the allegations levelled against him,” Gul said.
Gul said he was no longer representing Butt and other lawyers were now handling his case.
An ICC code of conduct tribunal will hear charges of spot-fixing leveled against Butt and pace bowlers Mohammad Amir and Mohammad Asif from Jan. 6-11.
The trio were suspended pending an investigation into allegations that they arranged for deliberate no-balls to be delivered in the fourth test against England this year.