The 82-year-old, who rose to fame in the 1970s as a "glam-rock" star, is accused of abusing the girl between 1978 and 1981 when she was aged eight to 11.
Prosecutor Jonathan Polnay told Westminster Magistrates' court that the offences had taken place at Gadd's home in the Kensington area of London.
The alleged victim, who lived nearby at the time, went to police in 2025.
Polnay said, when interviewed, Gadd had given a prepared statement in which he denied the offences and when shown a photograph of his accuser, denied knowing her.
He faces charges of unlawful sexual intercourse with a girl aged under 13, and three counts of indecent assault on a girl aged under 14.
Gadd, who appeared by videolink from prison wearing dark glasses, spoke to confirm his name and date of birth, also telling the court he was "extremely deaf" and could not hear anything.
He was remanded in custody until his next court hearing at London's Old Bailey on September 2.
The former pop star is currently serving a 16-year jail sentence imposed in 2015 after he was convicted of sexually abusing three schoolgirls between 1975 and 1980.
He was released on licence in 2023 but recalled to prison weeks later for breaching licence conditions.
He was first jailed in 1999 for possession of child pornography and later moved to Cambodia, but was deported in 2002 due to suspected sex offences.
In 2006, a Vietnamese court convicted him of committing obscene acts with two girls aged 10 and 11 and sentenced him to four years in jail.
On his release he returned to the United Kingdom.
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