Berlusconi is being tried in Milan on charges of bribery and the prostitution of a minor. The former leader testified Friday he never had an intimate relationship with the teen prostitute known as Ruby, who was 17 at the time the accusation was made in 2010.
During his testimony, Berlusconi said Clooney can help prove his claims.
Ruby has claimed she saw Clooney and his ex-girlfriend at one of Berlusconi's "bunga bunga" parties, which allegedly include lavish orgies, ABC News reported Sunday.
Clooney said he never partied with Berlusconi.
"I spoke to their people and said, 'I will come and testify if you'd like,' because I wasn't at the party that I was said to have been at. I wasn't at his 'bunga bunga' party," Clooney said in an interview with Time magazine last year.
Legal analyst Jean Casarez told ABC News Clooney's testimony would earn the defense some respect.
"To have a big movie star come from Hollywood all the way to Italy to testify on your behalf, I mean that's credibility for you," she said.
If convicted Berlusconi could be sentenced to a possible 15 years in prison.
Berlusconi resigned because of Italy's economic crisis in November.