The pair, along with defender Dejan Lovren, swapped the South Coast for Merseyside in the summer after signing for Liverpool.
The return of the two England internationals has dominated the build-up to Sunday’s Premier League clash – but Saints boss Koeman is not interested.
"It's not my question, my question is to prepare the team for the Sunday game," he said at his pre-match conference.
Saints boss Ronald Koeman
"I don't talk about players who are coming back to the club where they played last season, because then I can talk every week about a player who comes back to Southampton."
The Dutchman continued: "Lallana is a very good player, doing well in Liverpool. He chose to change the club after a good opportunity and nothing else.
"It is Southampton against Liverpool, not Southampton against some players who played last season for Southampton."
One England international Koeman was happy to talk about was Jay Rodriguez.
The striker, who made his Three Lions debut against Chile in 2013, has not played for 321 days after rupturing an anterior cruciate ligament last season, but he could be making a return shortly.
Rodriguez ruptured his anterior cruciate ligament
"It's a long way now for Jay and if it happens in March we are very happy," Koeman said. "If it happens in April we will see but at the moment not because he needs more time.
"I hope that Jay can still play some games in this season, but it is all about the freshness and the shape of the player.
"We don't take any risk because the player is too good to take that risk.”
