The controversial speedster underwent scans at the Shaukat Khanum Memorial Hospital on Wednesday and reports indicated swelling in the rib.
"The scans have proved the truth that I did not feign injury during the match. I have swelling on the 11th rib," Shoaib was quoted as saying in local daily The Nation.
"I have always done justice to my job and given my 110 per cent. I had a fall during bowling in the first innings and I injured my hand as well as my back. I informed about my injury to the captain and the manager," he said.
The daily said the four-member medical inquiry panel had detected the injury, and if it is officially confirmed, it could turn out to be a major embarrassment for top PCB officials including its chairman Shaharyar Khan.
The injury in Shoaib's rib was confirmed by sources close to the commission.
Asked about how he managed to bat on the fourth day of the Test if he was really injured, Shoaib said bowling requires a run-up from 40-yards and delivering the ball with certain force while batting involves less strain.
"During bowling the whole body has to be pushed very hard but the case of batting is different and before batting I had taken some pain killers," he said.
He also denied any differences with skipper Inzamam-ul-Haq, who had questioned his sincerity, and said, "we play for our country not for personal gains."
All-rounder Abdul Razzaq, who had also appeared before the medical commission on Wednesday, said that he would not play in the English County season in view of the injury and take a month's rest instead.
"I am feeling 70 percent fit now although I have started light training. I will go all out for bowling practice from next week. I will not be travelling to play in the English County this year and will be staying with the team," he said adding that he had explained about his injury to the commission.
Meanwhile, Shoaib's former coach Sabih Azhar has given his charge the clean chit.
"I know him since he was a child and I can tell you that he will never feign an injury," said Azhar, who now coaches the Rawalpindi team.
"He has won us many matches from hopeless situations and I can tell you he is hard working and will never shy away from a challenge. Although I haven't met him for long, I am sure injury would have forced him out. Otherwise, it is hard to believe that he would do such a thing."