Gul, 29, began the last phase of his rehabilitation programme at the national cricket academy on Friday (July 26) and said he was missing playing for the Pakistan team.
"It has been a frustrating time for me and I miss being with the Pakistan team. But right now I am just concentrating on regaining full fitness," he said.
Gul, who is the most seasoned pacer in the present Pakistan team with 163 Test, 161 ODI and 74 T20 international wickets, underwent a knee surgery in May in Australia after complaining of severe pain and swelling in his right knee during the tour to South Africa early in the year.
"I would say he requires another four to six weeks before he can get back to bowling," PCB doctor Dr Sohail Saleem said.
"Right now we have just started putting pressure on both his knees so it remains to be seen how he responds but his rehabilitation program has gone well so far. We will not rush things where his fitness is concerned," Saleem said.
The PCB decided to send Gul to Melbourne for the surgery after MRIs confirmed tear of the posterior horn of medial meniscus with patchy bone bruising on his right knee.
Gul said he hoped after the surgery the knee would not trouble him again and allow him to bowl at full pace.
"In South Africa and even before that the knee had started playing up and it did affect my bowling form and rhythm," Gul said.