According to media reports, the Spanish government is said to have rejected or at least delayed the appointment of the previous nuncio in Indonesia, Piero Pioppo.
The nunciature in Madrid has been vacant since March, after the previous nuncio Bernardito Cleopas Auza was transferred to the Vatican embassy to the EU.
The Italian online platform "Silere non possum" first reported on Tuesday that the appointment had failed.
The reasons for the alleged rejection of Pioppo, who is considered conservative, are not known.
The Spanish specialist magazine "The Diplomat", on the other hand, wrote of contradictory information from sources in the diplomatic environment.
While Vatican circles are said to have reported a "discreet blockade of the process without public statements" by the Spanish government, government circles have denied this.
Tense relationship between state and church in Spain
Pioppo has been nuncio in Indonesia since 2017. Born in 1960, the Italian priest is a longstanding Vatican diplomat.
After initial posts in Korea and Chile, he worked with the then Cardinal Secretary of State Angelo Sodano and was prelate of the Vatican Bank from 2006 until his appointment as nuncio in Cameroon.
The apparently imminent transfer to Spain has not yet been officially announced; according to diplomatic custom, the personal details are only made public once agreement has been reached with the receiving country.
The relationship between the Church and the government of socialist Prime Minister Pedro Sánchez is currently strained. This is due to calls for new elections by the chairman of the Bishops' Conference, Archbishop Luis Argüello, following a series of corruption scandals in the ruling party.
Questions of compensation for victims of abuse and the handling of the "Valley of the Fallen", the original burial site of the dictator Francisco Franco and the location of a basilica and a monastery, have also caused controversy for years.