But Koeman is convinced Southampton are able to push on again and believes Alderweireld, who made 26 League appearances last season, could be key to that.
For much of last season the Saints had the best defensive record in the top flight.
Speaking earlier this week, Koeman said: “The player likes to stay, we like to keep the player but it’s a little difficult at the moment with Atlético Madrid. I have a good hope he will stay for Southampton.