In a what has been viewed as legal setback for Bill Cosby, a judge has ruled that an additional woman who says he sexually assaulted her will be permitted to testify at his trial later this year.

Prosecutors had wanted to call up to 12 other women who claim the 79-year-old comedian assaulted them as they try him over an allegation that he abused a member of staff at Temple University in Philadelphia in 2004. They wished to do so to try and prove, the actor had a history of similar “bad acts”.

But in what may be a pivotal ruling, a judge said prosecutors can only call one other woman.

Bill Cosby at a court appearance last year in Philadelphia (AP)

Mr Cosby is set to go on trial in June over a 2005 complaint by former Temple University employee Andrea Constand, who is now a massage therapist in Toronto. Mr Cosby has denied any wrongdoing.

Prosecutors reopened the case in 2015 after newly released court documents showed Mr Cosby admitting he gave drugs and alcohol to young women before sex over a 50-year period, the Associated Press said.

Bill Cosby appears in court

The prosecutors had chosen 13 women from around nearly 50 who have accused the celebrity of assaulting them and asked Judge Steven O’Neill of the Court of Common Pleas, to admit their accounts as evidence. The prosecutors said the testimony was important in showing a pattern of conduct by Mr Cosby that bolstered the account of Ms Constand.

But the New York Times said that the judge only agreed to allow the testimony of one woman, identified simply as “Prior Alleged Victim Six,” in a one-page decision.

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The judge said that he made his decision after a consideration of the evidence and legal arguments presented by both sides and “following a careful balancing of the probative value of the other acts evidence and the prejudice to the defendant.”

Ms Constand has said that Mr Cosby drugged and sexually assaulted her at his home near Philadelphia. The star of iconic shows such a the Cosby Show has claimed that the encounter was consensual.