Gareth Senior carried out the attack in an upmarket Leeds city centre store when he spotted Mr Dorigo and new girlfriend Claire Joss together when his suspicions that they were seeing each other were confirmed.
Senior pushed his love rival into a towel display at The White Company before headbutting him in the face.
Leeds Magistrates' Court heard the attack happened on February 6 this year in the Victoria Gate store.
Senior had been in an 18-month relationship with Ms Joss which ended two months earlier.
The court heard the relationship began to deteriorate after Senior introduced her to Mr Dorigo at a music festival in Manchester.
They had both left their partners to be together.
They broke up shortly before Christmas last year and Senior became suspicious that she had been seeing the former Leeds United left back.
Senior went to confront the pair after spotting Ms Joss meeting a man as he left work.
He ran into the shop and up the stairs to the first floor when he realised the man was Mr Dorigo.
The incident was captured on CCTV which was played to the court.
Senior faces losing his job after being convicted of assault occasioning actual bodily harm.
Mr Dorigo described the assault when he gave evidence today.
He said: "I was looking at the towels at the back of the shop. The next thing I heard some shouting from behind.
"I didn't realise what was going on and I felt an excessive shove from behind."
He described how Senior then headbutted him to the face.
He added: "I managed to move back or else my nose would have been broken.
"I thought there was a bit of blood inside my lip. He was swearing and saying all sorts of things at this stage. I didn't really catch it all."
Ms Joss told the court she was returning an item at the till when she heard shouting.
She said: "Garth was shouting over the top of me. Words to the effect of he was going to kill Tony.
"Something along the lines of 'I knew you were after her'."
Ms Joss admitted that she "clouted" Senior twice as he stood at the top of the stairs after the attack.
She said her former partner continued to shout threats outside the shop.
She told the court: "We were stood outside of the main door. At that point he said it wasn't over and he was going to break his legs.
"He was clearly angry and saying other things. I got the attention of the security guards."
Senior had offered to plead guilty to a lesser charge of common assault at earlier hearing but it was rejected by the Crown Prosecution Service.
The court heard Senior had considered Mr Dorigo to be one of his heroes until he found out he was seeing Ms Joss.
His solicitor, Stuart Field, asked Senior: "If someone had asked you 18 months ago about Tony Dorigo what would you have said?"
The defendant replied: "I would have said in the context of football, and I still say it now, that he is probably one of the best left full-backs that Leeds United has had."
Mr Field asked Senior: "Did you assault Tony Dorigo?"
He replied: "Yes. I did. By pushing him."
The lawyer then asked: "Did you make any contact with his face." Senior replied: "No."
Deputy District Judge Paul Currer said he was satisfied beyond reasonable doubt that Senior had headbutted Mr Dorigo.
He said: "I am very sorry to see a man of your previous good character and good standing coming before the court in circumstances such as this.
"This represents something of a personal crisis that you went through in the last couple of years."
Senior, of Mozart Way, Churwell, was fined £500 and ordered to pay £100 compensation to Mr Dorigo, plus £300 court costs.