Ronan Curtis revealed he’s quipped with Shane Long that Southampton will be relegated this season.
Ralph Hasenhüttl’s side are currently in a dogfight to save their Premier League status.
Southampton sit in the drop zone with 12 matches remaining, although they are just one point from safety ahead of their trip to Arsenal on Sunday.
Meanwhile, the Blues are pushing for League One promotion.
While they play for rival clubs, Curtis and Long are both part of the Republic of Ireland set-up.
The Pompey winger was handed his senior bow against Northern Ireland in November, with the experienced Long also featuring.
When on Green Army duty, Curtis told how he joked with the striker that Southampton could be playing in the Championship next term.
But former Derry City talent also heaped praise on his Eire team-mate.
Curtis told Express FM: ‘I’ve seen him a couple of times.
‘We had a bit of banter, me and Shane, around the dinner table.
‘It was about they might get relegated and stuff, so I was taking the hand out of him although he was saying “We’re flying”.
‘He’s a nice bloke even though he plays for Southampton! Don’t underestimate him.’
Curtis will be hoping for another Republic of Ireland call-up during next month’s international break.