"Let me make a decision soon," the king told reporters outside the national palace.
The king had given political parties until 2 p.m. (0600 GMT) on Tuesday to put together alliances needed for a majority.
Significant election gains by an Islamist party added to investors' fears, notably over policies on gambling and alcohol consumption.
Its electoral gains have also raised fears in multicultural Malaysia, which has significant ethnic Chinese and ethnic Indian minorities following other faiths.
Anwar's coalition won the most seats in the Saturday election with 82, while Muhyiddin's bloc won 73.