The university has asked a Los Angeles judge to order the Oscar-nominated star to hand over the painting it claims the actress bequeathed its Austin campus.

O'Neal's spokesman said the portrait was one of two Warhol made of the Charlie's Angels star in 1979.

Arnold Robinson added the legal action was "completely ridiculous".

The university had hired investigators to track down the Warhol portrait,. However, its whereabouts was discovered after O'Neal's current reality TV show revealed it to be hanging above his bed at his Malibu home.

In a statement, Mr Robinson said the university had known for more than a year that the actor had the painting, which is thought to be worth $30m (£18.7m).

"Ryan O'Neal's friendship with Andy Warhol began 10 years prior to his meeting Farrah Fawcett," Mr Robinson said.

"When Ryan introduced Andy to Farrah, Mr Warhol chose to complete two portraits of her, one for Ms Fawcett and one for Mr O'Neal."