With results still coming in slowly from Tuesday's presidential and parliamentary elections, the millionaire former AC Milan striker and his main rival, Harvard-trained economist Johnson-Sirleaf, remained the frontrunners.
Electoral officials and observers said it looked increasingly likely that the presidential poll, the first since the end of a brutal 14-year civil war in Liberia, would have to go to a second round next month.
"It seems obvious to me personally that there will be a run-off now tentatively scheduled for 8 November," former US president Jimmy Carter, one of 400 international election observers, said on Thursday.
National Elections Commission chief Frances Johnson-Morris made the same prediction as she cautioned that final election results could take up to a week.
But excitement remained high on the streets of the crumbling capital Monrovia. Crowds gathered around radio sets, sending up a cheer with each new report of fresh gains by Weah or other favourite candidates.
With about 10% of votes tallied so far, 39-year-old Weah lead the field of 22 presidential hopefuls with 26.6% of the vote, ahead of Johnson-Sirleaf with 16.2%.
If no candidate gains more than 50%, a run-off will be held no more than two weeks after official confirmation of the first round's results.
If 66-year-old grandmother Johnson-Sirleaf wins, she would become Africa's first elected female president.
Liberians are desperate for the polls to return the West African country to stability two years after the end of the war, which killed a quarter of a million people and left infrastructure in ruins.
While Weah, dubbed King George by supporters, has amassed a huge popular following because of his star status, Johnson-Sirleaf is known as the Iron Lady because of her feisty style and her solid financial and government experience.
Some question whether the soccer star has the qualifications and political experience to be president. His supporters retort that Harvard-trained professionals such as Johnson-Sirleaf have done little to help ordinary Liberians over the last years.
Both Weah and Johnson-Sirleaf have said they would work together with whoever wins the presidency and have pledged to make reconstruction their priority.