Koeman was active during the most recent window, as he brought in the likes of Graziano Pelle, Dusan Tadic and Toby Alderweireld to help cover a mass exodus during the close-season.
Key players such as Luke Shaw, Adam Lallana, Rickie Lambert and Dejan Lovren all left St Mary's Stadium, although Southampton have coped well since and sit fourth in the top flight.
However, with Jay Rodriguez injured and Emmanuel Mayuka and Sadio Mane due to represent their countries at the Africa Cup of Nations in January, Koeman feels there is a need for reinforcements.
Having already agreed the loan arrival of Eljero Elia from Werder Bremen, Koeman is also eager to tie up the futures of fellow loanees Alderweireld and Ryan Bertrand.
"I think only to bring in players, not to lose players," he said on Wednesday.
"We spoke inside with everyone about the team, the positions. If we need another player it will be an attacker.
"Elia is a good signing for us because I like that player, it's part of our way of playing. We like to play with wing players, fast players.
"The situation is clear, I spoke to Toby that I would like him to stay but it's up to the player. He will get time to think on his future but, like Bertrand, we want to keep those type of players.
"They are showing their qualities already this year and we'd like to keep that."
Southampton face Arsenal on the south coast on Thursday with the sides separated only by goal difference and both tipped to secure a top-four berth this season.
Koeman acknowledged his delight at how the season was progressing but urged his side not to let up.
"Yes, everyone is delighted by the way we played the first half of the season, the points we have are well deserved and [it] shows the club is growing," he added.
"We like that because we do everything for that, we keep going. The philosophy is to bring in young players and a lot made their debuts.
"It's very good but we have to go on."
