Fr Lucio Angel Vallejo Balda was allegedly caught communicating with the outside world, according to the Vatican.
The Italian newspaper, La Repubblica has reported that he had telephoned a relative, as well as a show business agent.
Before he was granted house arrest, the priest had been held in Vatican cells since his arrest in November 2015.
He had been arrested alongside Francesa Chaouqui, a PR expert, accused of giving information to two journalists.
The pair were both members of a special commission set up by Pope Francis to clean up and the Vatican's finances and create a more transparent system.
Fr Lucio Angel Vallejo Balda and Francesa Chaouqui are being tried, alongside two Italian journalists.
The trial resumed Saturday following its adjournment last year.
Francesa Chaouqui, who is thought to be pregnant, has not been held in custody. She has been asked to be freed from a confidentiality clause before giving evidence in court, according to The Times.
Fr Balda is also being sued by Mrs Chaouqui for saying that he had sex with her and that she bullied him into releasing documents.
She faces up to eight years in jail if she is convicted in the Vatican court of leaking documents.
Speaking at the time of their arrest the Holy See said in a statement: "It must be remembered that divulging confidential documents is a crime under the criminal code of the Vatican City State (Law IX, art. 10 and art. 116 bis c.p. - passed 13 July, 2013).
