Former Leeds star Tony Dorigo described how his love rival could have broken his nose if he had not managed to back away as he was headbutted.
Giving evidence, Mr Dorigo confirmed that he had met Senior on two occasions before the attack.
He said he had met him for the first time at the music event in Manchester and had seen him on a second occasion during a dinner he was giving a speech at at the Queens Hotel in Leeds.
Prosecutor Gareth Henderson-Moore asked him: "When you first met Mr Senior was he in a relationship with your partner?"
Mr Dorigo replied: "Yes."
He described how he fell forward about four or five feet after being shoved in the back by Senior.
He said the defendant's forehead then made contact with his face.
He said: "He just headbutted me. I didn't really know what was going on and at that point it was all a bit of a shock.
"He caught me on my nose and top of the lip.
"I thought there was a bit of blood inside my lip."
Mr Dorigo said his eyes began to water after the impact and he suffered soreness for a few days afterwards.
During cross-examination, Senior's solicitor Stuart Field said: "I have to put it to you that, because of the shock and surprise, you have magnified the extent of your recollections of it and that there was no headbutt?"
Mr Dorigo said: "There was a headbutt."
Mr Field showed a picture to the court, taken four days after the incident, of Mr Dorigo in the Legends Lounge at Elland Road before Leeds United's game against Sheffield United.
Mr Field asked Dorigo if he agreed that the image appeared to show that he had no visible injuries.
Mr Dorigo said he did not have injuries but just felt sore.
Australian-born Mr Dorigo played made 171 appearances for Leeds United between 1991 and 1997.
He was voted Fans' Player of the Year in their First Division title-winning season in 1992.
He was capped for England 15 times and also played for Aston Villa, Chelsea, Torino, Derby County and Stoke city.