Pakatan Harapan is expected to name its candidate for prime minister next month, said DAP secretary-general Lim Guan Eng.
He said the candidate will be replacing the coalition's majority choice for prime minister, Anwar Ibrahim, as he is still behind bars.
"Our choice is of course for Anwar to be prime minister, but he is still in prison, so that is impossible.
"So we have to have a different candidate. A choice will be made, and we hope to announce it next month," he was quoted as saying by Sinar Harian.
During a retreat earlier this month, it was reported that Harapan had suggested its chairperson Dr Mahathir Mohamad become prime minister on an interim basis with PKR president Dr Wan Azizah Wan Ismail as deputy premier.
Both PKR and Mahathir have insisted that the proposal was not final.
Anwar is serving a five-year prison sentence after being convicted of sodomy.
He is expected to be released on good behaviour sometime next year, but will still be ineligible to run for Parliament.