A total of 22 former international cricket captains - also including Sunil Gavaskar and Kapil Dev of India - have signed the second such letter in six months to Pakistan prime minister Shehbaz Sharif.
The latest appeal comes days after Khan was taken to a government hospital in the capital for a medical examination.
His examination was conducted in the presence of one of his sisters, and Khan was then returned to Adiala prison in the garrison city of Rawalpindi. Doctors declared him 100 per cent medically fit.
However, the group of cricket greats questioned the procedure of Khan's medical check-up.
"Pakistan's Supreme Court ordered that Imran Khan be transferred to hospital for examination by a medical board that was to include his own personal physicians and his sister, Dr Uzma Khan," the cricketers said in the letter.
"Concerningly, Mr Khan's hospital stay lasted only a few hours. He was examined by a state-appointed team rather than the board the court had directed, declared 'medically fit,' and returned to Adiala jail before that board could complete its work."
Khan, 73, led Pakistan to the 1992 Cricket World Cup title and served as prime minister from 2018 until he was ousted in 2022.Â
The 22 former national team captains said they did not seek to adjudicate on Pakistan's domestic legal process and had written to the prime minister "not as politicians, but as former colleagues and rivals (of Khan) who share a bond forged on the cricket field".
In February, 14 former international cricketers expressed their concern over Khan's health after his family said he had lost around 85 per cent of the vision in his right eye, a claim disputed by the government.
Authorities later said his condition was improving following treatment.
Khan's lawyers and family have also accused the government of defying a court order that required him to be examined at the private Shifa International Hospital in Islamabad.
Pakistan's government rejected the allegations over the weekend, saying Khan was examined by doctors from the private hospital and that he could not be taken to Shifa International for security reasons.
The government said Khan's supporters had begun gathering outside the private hospital in violation of the court order, which required them to stay away from the medical facility to avoid inconveniencing other patients.
