"The issue of who will lead the Senate will be decided on the basis of which group or aspirant has the numbers to win the fight," Pimentel said.
Congress resumes on May 15, when the issue of the Senate presidency will be tackled.
Pimentel did not discount the possibility that the status quo may prevail if nobody can muster the minimum of 13 votes to wrest control of the Senate leadership.
It will take 13 votes to replace Drilon, he noted, adding that no party or group in the Senate has the votes to elect a new Senate president.
"Drilon has maybe five senators; Villar, four; (the) opposition, seven; and unidentified flying objects, seven. The Senate presidency is anybody’s ballgame," Pimentel said.
Last Wednesday, Sen. Juan Ponce Enrile said the Senate presidency remains a matter of "numbers" even if there is an existing "gentleman’s agreement" between Drilon and Villar.
"The Senate presidency is a function of the chamber and it is a question of numbers. If Frank Drilon, being a party to the gentleman’s agreement, will voluntarily relinquish, then Manny Villar will be free to seek the position. I do not know if there is anyone who will challenge him," Enrile said.
Enrile was confident that Drilon would also support Villar if he finally decides to relinquish the post.
"I suppose even the Senate president now will support him if he finally decides to honor his commitment," Enrile said.
When asked, Enrile, a veteran lawmaker, revealed that he is not interested in the Senate leadership and echoed the statements made by Senators Joker Arroyo and Richard Gordon that they are not bound by the gentleman’s agreement between Drilon and Villar.
"I am not party to the agreement," Enrile said, adding that he is answerable to the Filipino people who voted him into office as senator.
Enrile explained that neither Villar nor Drilon could decide for the chamber as a whole. The matter will "have to be submitted to the chamber for voting," he said, adding that senators are not bound by any agreement.