The conservative People's Party (PP) and the far-right party Vox, a potential coalition ally, would still win enough seats for an absolute majority in the 350-member lower house, two polls released on Monday showed.
All polls have found the PP would need support from Vox to form a government.
The PP would win between 150 and 154 seats, according to a GAD3 poll for ABC newspaper carried out on June 29-30.
An earlier GAD3 poll conducted between June 5 and June 8 had given the PP between 150 and 153 seats.
A third poll by 40DB, hired by El Pais newspaper, showed PP and Vox falling short of the 176 seats required for an absolute majority.
Persons:
Vox, Pedro Sanchez, Podemos, GAD3, El, 40DB, Inti Landauro, Charlie Devereux, Gareth Jones
Organizations:
Socialists, PSOE, People's Party, Vox, Sumar, ABC, IMOP, El Pais, Thomson
Locations:
MADRID, 40DB's