The onus will certainly be on John Egan when Ireland line-up for their upcoming Euro 2020 qualifiers.
Ireland won't be able to avail of the regular centre-back pairing for October's games against Georgia and Switzerland, with Shane Duffy and Richard Keogh both injured for vastly different reasons.
Egan is next in line to anchor the defence, most likely alongside Burnley's Kevin Long. Both played together against Bulgaria in a friendly in September - Egan as captain - but are relatively inexperienced when it comes to competitive international games.
Former Ireland manager Brian Kerr liked what he saw from Sheffield United's Egan and his team-mates against Liverpool on Saturday.
"What we saw was excellent defending, brave defending, blocks and tackles and cohesive work between the three of them to shut out Liverpool for most of the match," he said.
"Egan, given his performances will probably come in to Mick's team now that he has the problem at centre-half - both of them being out. So Egan could be an important performer."
As Kerr pointed out, the Cork-born defender plays in a vastly different defensive system for Sheffield United.
"Now, he's in there and he looks comfortable. But it's a bit different at international football if you're playing in a two," he said.
"Mick generally plays with two centre-halves, a bit different from playing a three as we saw with Newcastle [on Sunday]. With three, there's usually a bit of a comfort zone because you can fall in to a five at the back as well.
"So there would be a lot more pressure on him I think. If you're playing a higher level, with a team where there's an expectancy to be on the front foot which there will be with Ireland, maybe not in the next two games though. But we can't afford to sit back against Georgia.
"And it's not Mick McCarthy's style. I was like that myself as a manager. I didn't like to see my team on the back foot or in our own half too much. To play that way, the centre-halves don't have to be the quickest.
"But they have to be very sharp in their judgement and quick on their feet on the turn and not caught flat-footed.
"So that's what John Egan's going to have to do. He wasn't overly impressive under the previous manager where a lot of the performances were quite scatty."
You can watch Brian Kerr's full chat on John Egan, Newcastle and more on our YouTube channel.