IRISHMAN Mark O'Connor was forced to apologise to Geelong officials after they discovered he played a recent Gaelic football match without the Cats' permission.

O'Connor returned home to Ireland after playing in Geelong's losing elimination final to Melbourne and lined up for Dingle in their Kerry county senior championship semi-final on September 29.

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The 21-year-old, who joined the Cats as an international rookie at the end of 2016, lasted just 45 minutes before he was sent from the field for a foul that resulted in a scuffle.

It was O'Connor's first competitive match of Gaelic football in more than two years.

AFL.com.au understands Geelong was unaware of O'Connor's participation until the days following the match, which prompted instant communication from senior football staff.

"It was down to the risk of injury which would then compromise his ability to play and train for Geelong," head of football Simon Lloyd said when contacted by AFL.com.au.

"We (told Mark we) cannot provide permission for you to play in further Gaelic football games as it's a breach to his contract."

"To Mark's credit, he acknowledged Geelong was his main priority and that he wouldn't do it again."

Geelong's strict instructions to O'Connor came before Carlton's Irishman Ciaran Byrne suffered a serious leg injury playing Gaelic football last week after retiring from the Blues.

O'Connor was absent from the Cats' best and fairest count on October 4, granted leave by the Cats to return home to Ireland.

After five games this season, including the last four consecutive matches, O'Connor remains contracted at GMHBA Stadium for 2019.