Schneiderlin is set to miss the rest of the season with injury and interest is reported to be mounted in his services.
The likes of Tottenham Hotspur and Arsenal are both expected to make moves for the French international in the coming months, if reports in the Daily Mail are to be believed, and Koeman admits that he could be powerless to stop the defensive midfielder from leaving St. Mary's.
Southampton are understandably keen to keep Schneiderlin, who has become one of their most integral players, but Koeman says there is only so much he can do to keep him at the club and out of the clutches of a rival.
“It’s more difficult, it’s more difficult,” he said. “I understand, because I got the possibilities to change the team and to go to a big team from Holland – to Barcelona at that time – but I understand, it’s difficult.
“We try, we try, but we try to keep him longer than he is normally, and that is for the rest of the players as well – we do everything.
“But there is a stop that we can’t do more and then it’s all about the decision of the player.”
The 25-year-old provides good protection for his side's defence, but he also has the ability to dictate play and it is no surprise that he is so in demand.
Southampton are no strangers to losing key players, and have generally replaced them well, but finding adequate cover for Schneiderlin could be tough.