Despite a string of close-season departures, Southampton have surprised to be sitting third in the Premier League table.
But a busy December, when they play seven games in all competitions, looks set to test Southampton's top-four credentials.
Koeman knows finishing in the top four will be difficult, but he intends to ask for January additions to help his side.
"I will speak to the board of the club, about what we need and what we would like to do," the Dutchman said.
"This is the hardest league because you can lose against everybody. You have to be prepared every game and you can't play on 70 per cent.
"You have to be 100 per cent and that's difficult for us, because we need everybody.
"Everybody needs to be fit and we don't have the numbers and players that the big teams have, and that's difficult."
Ahead of Wednesday's clash at Arsenal, Southampton are two points clear of fifth-placed West Ham and six ahead of Arsene Wenger's men, Liverpool and Tottenham.
Koeman is worried a lack of experience, and a different mentality, could hurt his team as the season goes on.
"The club also does not have the experience of top-four football like the other clubs. That is the difference at the moment, we don't have that mentality," he said.
"We want to have that, though. The club wants to stay in the position where we are now, everybody wants that.
"But it is so difficult because we have different kinds of squads. We have younger players with good ability but not as much experience.
"One day we will have our foot on the pedal and will always be challenging them, but it is a long way to go."
