MONROVIA, Liberia — A former professional soccer player and the incumbent vice president are leading in the first round of Liberia’s presidential election, partial results show, and may face each other in a runoff.

With votes from around 25 percent of polling stations counted, George Weah, once named African Player of the Century, and Vice President Joseph Boakai emerged as the top vote-getters among the 20 candidates in Tuesday’s election. Mr. Weah, with roughly 136,000 votes, was leading Mr. Boakai, with 105,000 votes.

But it was unclear whether Mr. Weah would be able to ultimately capture 50 percent plus one vote, the threshold to avoid a second round of balloting.

If no one reaches that level, the top two candidates will advance to a runoff election next month. They are seeking to replace Ellen Johnson Sirleaf, who is stepping down after two terms as Africa’s first democratically elected female president.