Bersatu chairperson Dr Mahathir Mohamad will meet jailed PKR de facto leader Anwar Ibrahim tomorrow, three days after being named as Pakatan Harapan's prime ministerial candidate.

The meeting will take place at Cheras Rehabilitation Hospital where Anwar is recuperating after a shoulder surgery in November last year.

The planned visit was revealed in an invitation by PKR to the media this evening.

Following Mahathir's naming as prime ministerial candidate at the Harapan convention last Sunday, he has faced grumblings, particularly from certain groups in PKR.

Selangor PKR information chief Hizwan Ahmad had spoken out against the announcement, while PKR Wanita chief Zuraida Kamaruddin, who is also Selangor PKR chief, insisted that Mahathir should instead only be appointed a "senior minister."

This was despite Anwar saying, in a special message read out by his daughter, PKR vice-president Nurul Izzah Anwar (photo), that he accepted the coalition's decision and that it would not derail reforms.

However, he did not specifically mention Mahathir in the message.

Mahathir, in his acceptance speech, had thanked Anwar and said he was indebted to the man whom he once sacked as his deputy prime minister and jailed for sodomy and corruption.

Anwar was freed in 2004 after his sodomy conviction was overturned, but was jailed on a similar charge in 2015.

Anwar claimed the charge was politically-motivated while Putrajaya denied any such conspiracy against him.

The opposition icon is due to be freed from prison on June 8.