With Fraser Forster out injured for a considerable amount of time, the Saints have a limited amount of cover and Koeman admits that they are thinking about bringing a new stopper in over the summer to increase competition.
"Of course we have thought about it," he said. "Maybe we need a goalkeeper, because we have to make decisions. We have to make decisions about [whether] our young goalkeepers [are ready to make the step-up] and our plans for next season."
Reports in the Mirror this week have suggested that their main target is Reading 'keeper Adam Federici, but Koeman insists that there is no truth in these rumours.
It means that the identity of Southampton's target is unknown, but it seems that a new custodian will be on the club's wishlist when the transfer window reopens.
That puts Forster's position as the Saints' number one under threat and he will have to prove himself when he does return from injury.
The former Celtic man has been hugely impressive since arriving at St. Mary's at the start of the season, but with increased competition pressure will be on him to return to the top of his game.
If he does then it will be difficult for whoever is brought in to permanently displace him, but Forster will realise that he will have to show few signs of rustiness if he is to win his place back.