The Gambia's Supreme Court is unable to hear the petition seeking to annul last month's election until May, chief justice Emmanuel Fagbenle says.
The Nigerian judge due to oversee the seven-member panel was not available till then, he said.
Longstanding ruler President Yahya Jammeh, 51, initially accepted defeat but later rejected the result.
It is not yet clear what will happen after Mr Jammeh's term ends on 18 January.
President-elect Adama Barrow is due to be inaugurated the following day. But Mr Jammeh has said he will not step down and he has the support of the head of the army.
West African leaders, led by Nigeria's President Muhammadu Buhari, are due in the capital, Banjul, on Wednesday in a last-ditch diplomatic effort to resolve the crisis.
But Mr Jammeh has rebuffed their attempts to get him to step down, saying they have no right to interfere.
Mr Jammeh lodged a case before the Supreme Court after the electoral commission changed some results.
The commission insists the outcome was not affected by an initial error and property developer Mr Barrow defeated Mr Jammeh.
The Supreme Court hearing had already been delayed once because of a shortage of sitting judges, and other judges from neighbouring countries have since been appointed.
But the Nigerian who was to act as the president of the court - Onogeme Uduma - is fully booked until May.
The Gambia, a popular tourist destination, has not had a smooth transfer of power since independence from Britain in 1965.
Mr Jammeh seized power in 1994 and has been accused of human rights abuses.