FIFA presidential candidate Michael van Praag has withdrawn from the May 29 election and has switched his support to FIFA vice-president Prince Ali bin al-Hussein of Jordan.
The Dutch football federation president said in a statement he will explain his decision at a news conference later on Thursday.
Former Portugal great Luis Figo remains the third candidate in the election.
Blatter is strongly favored to extend his 17-year reign with a fifth term when the 209 national federations vote next week.
Blatter has pledges of support from most voters in five of FIFA's six continental confederations. Only UEFA is formally opposing Blatter and has supported all three opponents who were declared as candidates in January.
It was long expected that at least one of Blatter's rivals would withdraw before election day to unify opposition.
Although Van Praag is a member of the UEFA executive committee, he has appeared to be the most independent of the three challengers.
He pledged to serve a single four-year term to modernise FIFA and improve transparency, and offered Blatter an advisory role heading a charitable foundation.
Outside Europe, Van Praag gained one pledge of support from the former Netherlands territory of Suriname.