O'Connor to miss Oldham clash
It's an unwanted blow as the Millers, unbeaten in six on their return to League One, aim to complete their best league start since the 1948/49 season.
And frustrated boss Steve Evans pointed out that it was not the first time O'Connor has reported back from an international fixture unfit.
He told the Advertiser: “As much as I'm in favour of players getting picked for their country, it is completely unacceptable that Michael goes away with Northern Ireland twice and comes back injured each time.
“The first time last month he broke a little bone in his hand and this time it's his groin.
“We are not at the heights of the Premier League, where this sort of thing doesn't matter. Michael O'Connor is a big player for us and in very good form. It is hard to take."
The Millers welcome back Kari Arnason from international duty with Iceland while defender Mark Bradley is also available again after injury. But another casualty, skipper Craig Morgan, is doubtful.
Full story, and much more on Rotherham United, in this week's Advertiser.