Matteo gained six caps for Scotland before retiring from international football citing that his knee would not be able to deal with the rigours of so much football.
The 29-year-old received a barrage of criticism from pundits north of the border, who claimed the former England U-21 international had never been committed to the Scots' cause.
But he told the Sunday Mail's Sport Monthly magazine: "I would love to be playing for Scotland without any problems but it just can't be.
"I visited a specialist in Munich called Dr Hans Mueller-Wolfhart and he painted a clear picture.
"He tried everything. I had goose liver, calf's liver and juices from a turkey's head injected into me.
"The bottom line was that something had to go and I decided to give up playing for my country.
"Leeds pay my wages and they have to come first."
Matteo added: "I'd had trouble since my days at Liverpool and actually failed my medical at Leeds.
"But David O'Leary wanted me and made sure the transfer went ahead."