The last election in 1990 was won by the National League for Democracy (NLD) led by opposition leader Aung San Suu Kyi, but the results were never honoured by the military, which has ruled the country since 1962.
An election boycott by the NLD would deal a a potential blow to the Myanmar government's promotion of the polls as part of a "roadmap to democracy".
The NLD said the new constitution of 2008 is unfair, containing clauses that would ensure the military remains the controlling power in government, and would bar Aung San Suu Kyi from holding office.
"Aung San Suu Kyi said if freedom of information and freedom of expression are not allowed, the elections will neither be free nor fair nor credible"
Nyan Win, her lawyer and NLD spokesman
On Friday Aung San Suu Kyi said she has not decided whether her party will contest the planned polls, according to her lawyer, Nyan Win.
Nyan Win, who is also a party spokesman, said Aung San Suu Kyi herself has not yet decided whether to participate in the election.
According to him, she said the poll cannot be credible unless the government allows freedom of information.
"Aung San Suu Kyi said if freedom of information and freedom of expression are not allowed, the elections will neither be free nor fair nor credible," said Nyan Win, after meeting her at her house on Tuesday.
The Nobel Peace Prize laureate is serving a new 18-month sentence of house arrest in a country where the military government tightly controls information.
"[She] said she is in no condition to decide whether the NLD should participate in the elections or not as she cannot follow up on her decision if she remains detained," Nyan Win had said earlier this week.
According to him, Aung San Suu Kyi also said the international community should understand that the elections in Myanmar cannot be considered as similar to those in other countries "as everything has to start from scratch", without any new parties being approved yet and her own party not yet allowed to reopen its district offices.
Meanwhile a UN human rights envoy is expected to visit Myanmar next week, days after the military government jailed a US activist in a crackdown on dissent.
1988: Military crackdown on pro-democracy protests, estimated 3,000 killed
1989: Aung San Suu Kyi sentenced to house arrest for allegedly endangering the state
1990: NLD wins landslide in national election; military refuses to recognise result
1991: Suu Kyi awarded Nobel Peace Prize
1995: Suu Kyi freed, but movements restricted
1997: Myanmar admitted to Asean
2000: Suu Kyi sentenced to house arrest for defying travel restrictions
2002: Suu Kyi released following UN-facilitated secret talks with government
2003: Government unveils "road map" to democracy; Suu Kyi returned to house arrest after her convoy is attacked in north of country
2005: Government announces shift to new capital Naypidaw
2007: Nearly 3,000 prisoners released in amnesty to mark independence anniversary, but no key political figures freed
Tomas Ojea Quintana is scheduled to start his five-day trip on Monday, including planned meetings with Nyan Win, Myanmar's foreign minister. He is not expected to meet Than Shwe.
Quintana, on his third visit to Myanmar after a mission last year was postponed, said he also wanted to meet Aung San Suu Kyi.
He said in a statement released by the UN human rights office in Geneva that 2010 was "a critical time for the people of Myanmar".
"I hope that my request to the government to meet with... Aung San Suu Kyi will be granted this time," he added.
"It would be important for me to meet with political party leaders in the context of this year's landmark elections."
In confirming Quintana's visit a Myanmar official said he would visit Sittwe, in Western Rakhine state, near the country's border with Bangladesh.
On Thursday European Union legislators passed a resolution urging China, India and Russia to use their might to pressure Myanmar to improve human rights and called on them to stop supplying arms to the regime.
The parliamentarians urged "China, India and Russia to use their economic and political leverage with the authorities of Myanmar in order to bring about substantial improvements in the country".
They also called on the three "to stop supplying the [Myanmar] regime with weaponry and other strategic resources".