"I don't know but it was wrong to expect them to be like Virat Kohli or AB de Villiers and perform like them," Afridi said on Geo News channel on Monday.
Shehzad and Umar, considered to be two of the country's best young batting talents, have been axed for the tour to England on disciplinary grounds and were not called for the training and skills camps set up by the cricket board.
PCB Chairman, Shaharyar Khan made it clear on Sunday that it was the decision of the new selection committee to sideline the two youngsters.
Afridi said there was no doubt that Shehzad and Umar needed to work hard on their cricket and approach.
"I also agree there should be no compromise on discipline. But I think it is best if we stop expecting too much from them and just let them be and let them play the way they do. With more experience I am sure they will be much better," he added.
"But don't expect them to perform like Kohli or de Villiers. Don't make such comparisons."
Afridi, who had stopped short of officially announcing his retirement from T20 cricket, said he has given himself another two years.
"I have given myself another two years of cricket as I am still enjoying the sport. Whether I play in foreign or domestic leagues or for Pakistan it does not matter. I have given myself two more years. Whenever the selectors need me for Pakistan I am always available for the country," he said.
Afridi said he was impressed by the way Inzamam had called him up and spoken to him about his future plans.
"It was a good and positive thing and showed respect for a player. I told Inzamam if he wants to try out youngsters he should do that but whenever he feels he needs me I am there to play for Pakistan."
Afridi stepped down as the national T20 captain in April after poor performances from the national team in the Asia Cup and World T20 events which also led to the resignation of head coach, Waqar Younis.
Asked about why he had backed tainted left arm pacer, Mohammad Amir's return to the team, but not Salman Butt and Mohammad Asif although the trio committed the same crime, Afridi said the crime was the same but in the post spot-fixing scandal the attitude of the three was different.
"Look I always felt that in Salman Butt we had found an opener and player who could fill in the gap left by Saeed Anwar and Aamir Sohail. I liked his game and his approach. So no one was more disappointed than me when the spot fixing scandal happened.
"But after the scandal when I spoke to Amir he admitted to his mistake and sought forgiveness from everyone. But I don't know for what reason Butt remained in a state of denial and that really hurt me a lot as the scandal had damaged the image of Pakistan cricket," Afridi added.