Umar Farooq is ESPNcricinfo's Pakistan correspondent
Naseem, the 16-year-old fast bowler who has played three Test matches since making his senior international debut in November, was named in the original Under-19 squad last month. Pakistan head-coach-cum-selector Misbah-ul-Haq and bowling coach Waqar Younis, however, were not in favour of releasing him for age-group cricket.
The senior and junior selection committees have now come to an agreement, and Naseem will not travel to South Africa for the tournament, which begins on January 17.
"The ICC U19 Cricket World Cup is a stepping stone for future stars and a platform for budding youngsters to graduate to international cricket," said Wasim Khan, PCB's chief executive officer. "Naseem has recently broken that glass ceiling and has established his credentials as an international cricketer. As such, the PCB has taken a pragmatic approach and decided to withdraw him from [the] competition to provide this opportunity to another promising cricketer so that he can show his mettle and potential at a global stage."
In his short time so far as an international cricketer, Naseem has marked himself out as a special talent with his precocious pace and venom. He made his debut in Perth, in the first Test of Pakistan's recent tour of Australia, and dismissed centurion David Warner with a brute of a short ball. He missed the second Test with a knee niggle that is understood to have hindered his rhythm in the nets, but played both Tests of Pakistan's home series against Sri Lanka, taking seven wickets in the two Tests including a match-winning five-wicket haul in the second Test in Karachi.
That performance made him the second-youngest bowler, behind compatriot Nasim-ul-Ghani in 1958, to take a five-for in Test cricket, and the youngest fast bowler to do so.
The junior team management, headed by coach Ijaz Ahmed, wanted Naseem to be freed up for the Under-19 World Cup, and he was meant to link up with his team-mates at a preparatory camp in Lahore after the series against Sri Lanka. But he did not attend the camp, and was also rested from the Quaid-e-Azam Trophy final in Karachi.
"This should not deter Pakistan's chances at next year's ICC U19 Cricket World Cup as the selectors have picked a side that is experienced and bubbling with confidence to perform strongly," said Khan. "Naseem will now remain in Pakistan and continue to work on his skills under the watchful eyes of bowling coach Waqar Younis. Furthermore, he will remain available for the home series against Bangladesh."
Pakistan, the 2004 and 2006 champions and three-time runners-up, are slotted in Group C along with Bangladesh, Scotland and Zimbabwe in the 16-team Under-19 World Cup. They will kick off their campaign against Scotland on January 19 in Potchefstroom.
After a month-long camp followed by a break, the players regrouped in Lahore on Wednesday for the final leg of the camp. The team will depart for Johannesburg on January 10 from Lahore.