The inspirational Duff accepted the injury, knowing it was only a matter of time until his hectic summer took its toll.
“Something has been coming for the last couple of weeks because my legs have felt tired,” he told the Evening Telegraph.
“I suppose all the travelling and everything else that goes with it has finally caught up with me.”
Souness, however, was visibly unimpressed at losing his star man.
“I make a comparison with having a factory, buying an expensive machine and someone comes along, picks the best one out and says, ‘I am going to take it away and the chances are it will return home broken. It’s your problem, not mine.’ What other business is there that works like that?” he quipped.
“To be fair to Mick McCarthy he has played ball with us. It’s not a personal criticism of him,” he added.
The Football Association of Ireland may even cough up £100,000 to cover Duffers wages, but this didn’t cheer the Scot up any.