McCarthy had accused Shiels of "lying or telling fibs" regarding goalkeeper Cammy Bell, who was reportedly a transfer target of Ipswich at the end of the current season.
"It was a lie if [Shiels] confirmed it," McCarthy told reporters. "Do you want me to say it again? There's no truth in it. He's lying or he's telling fibs. Is lying too strong a word?
"I've not spoken to him and if somebody from this club has spoken to him they've done it without me saying so. If that's the case then I'm going to be pretty cheesed. Does that clear that one up?"
However, today, Shiels has insisted that he was informed of Ipswich's interest in the keeper.
"I've done nothing wrong and Mick is wrong," he said. "Ipswich Town haven't spoken to me about Cammy Bell and I never said that they had. I just said that there was interest from Ipswich Town.
"Basically I got a phone call from an agent who said there was interest in Cammy Bell from Ipswich Town.
"I'm surprised Mick didn't ring me to say, 'What's happening here because you're saying we're interested in your keeper and it's not the case.' I expected some sort of call but it didn't come."
Bell, 26, has made one appearance for the Scottish national team.