A judge has thrown out a lawsuit against the owner of American Pharoah just days before the horse attempts to win the Triple Crown.

Howard Rubinsky sued Ahmed Zayat last year, claiming he owed him $1.65 million advanced for gambling bets placed at offshore casinos.

According to court papers, Rubinsky and Zayat entered into a personal services contract in 2003 and Rubinsky said he advanced Zayat credit at a couple of casinos under the agreement he would be paid back.

However, a federal judge ruled the six-year statute of limitations had expired in New Jersey.

"Justice always prevails," Zayat told the Associated Press.

"I have said before these are all lies from A to Z. And the judge ruled in our favour. Could not have happened at a better time."

In US horse racing's biggest week, Zayat's horse is chasing the first Triple Crown since 1978 when he races in the Belmont Stakes on Saturday (Sunday AEST).

Rubinsky claimed that by the end of 2005, Zayat owed him $2 million. Some has since been repaid. Zayat has denied owing Rubinsky the remainder of the money.

In his ruling, US District Judge William J. Martini sided with Zayat's argument that Rubinsky's claim dated to 2005, when Rubinsky hired an attorney and investigator to recover the alleged debt.

Rubinsky had said the claim dated to 2008, when he received text messages from Zayat that constituted a written promise to repay the $1.65 million.