Bhutto said that, despite pledges from Musharraf in the power-sharing talks to introduce democratic reforms, "on the ground, nothing has changed from nine months ago".
Bhutto expected her Pakistan People's Party's (PPP) members of parliament to resign.
Asked if that would be the decision, she replied: "Most probably.
"I think that the resignation of the Pakistan Peoples Party MPs will be a severe blow to the legitimacy of the presidential elections."
Although the PPP is the largest opposition faction, it is not in a position to stop his re-election. But it could damage the credibility of the process if it boycotted the vote.
She said she expected the final decision to be taken by her party later on Wednesday or Thursday.
"We don't want to resign. We don't want to take this step, but certainly we are being pushed into taking this step by the inability of the present regime to move towards the democratisation of Pakistan," Bhutto said.
Bhutto plans to contest parliamentary elections due by mid-January.
Faced with street protests and growing political isolation, Musharraf has been negotiating a power-sharing deal with Bhutto.
Among the PPP's demands are a removal of the ban on anyone serving a third term as prime minister, which would disqualify Bhutto.
Bhutto said there had been no movement on this and other issues, despite promises from Musharraf.
Bhutto has also disputed government claims that corruption cases against her has been dropped.
"This is just a typical disinformation campaign by the present regime," she told reporters in London.
Bhutto said Musharraf's continued rule in uniform was fuelling extremism in Pakistan.
"The longer the military regime continues in this fashion, the more anarchic the situation becomes," she said.
"I am afraid we are heading for a situation which could lead to street agitation."
Pakistani authorities opened Islamabad's Red Mosque on Wednesday, nearly three months after more than 100 people were killed when commandos stormed the compound to end a siege by radical students.
Hundreds of people turned up to offer prayers at the newly painted and repaired Lal Masjid, or Red Mosque, which was reopened on the orders of the supreme court.
An earlier attempt to reopen it sparked violent clashes between religious factions and police and a suicide bomber killed 13 people near the mosque on the same day.
But there was no trouble on Wednesday as police removed barbed wire and security posts from around the mosque.
The mosque's bullet-riddled walls and blasted outer walls have been repaired. The authorities had torn down the religious school after the siege.