Ronald Koeman has refused to be drawn on increasing speculation that Saints are set to mount a bid for Celtic defender Virgil van Dijk – but has confirmed the club will sign a centre half before the close of the transfer window.

Saints have already moved to secure the services of Steven Caulker on a season long loan deal, with the 23-year-old hoping for a competitive Saints debut in tomrrow night's Europa League third qualifying round second leg at Vitesse.

But with Florin Gardos facing six months out through injury and Toby Alderweireld having turned down a move to the club in favour of Tottenham, Saints only have three frontline central defenders in Caulker, Jose Fonte and Maya Yoshida.

Van Dijk has been linked with Saints in the past and is valued by Celtic at more than £7m.

Koeman would not confirm interest in the Dutchman but did admit he is very much in the market for a centre half.

“It’s a lot in the media about the player,” said Koeman of Van Dijk. “I think it’s the best in my position to say nothing about that, because everybody knows he’s a good player, it’s a lot of interest for the player. Let’s see what happens.”

When asked if Saints would look for a central defender Koeman confirmed: “Yes, we need one more in that position.”

Top of Koeman’s list of priorities for now though is making progress in the Europa League.

Saints are in pole position to do just that as they take a 3-0 lead to Holland for the second leg of their third qualifying round tie against Vitesse.

Should Saints make it through tomorrow night then they won’t have to wait long to learn who stands between them and the group stages of the competition with the draw for the play-off round taking place on Friday.

Koeman though is focussed on the Vitesse game.

“I hope for a good game and for sure a game that we will start with the same intensity what we did last week,” he said.

“Even with this result it is a comfortable result, but it is only after 90 minutes.

“Football is sometimes strange and if you don’t start with enough concentration, if you don’t play with the same intensity in pressing the opponent then it is possible that you get a difficult evening.

“But if we play at our level with the same concentration and the same intensity, the qualities make the difference.”

He added: “The best is to start again at zero.

“On one side don’t forget the last game and in the other side take your analysis about last week, why we had difficulties in the second half, why we create some good chances.

“It is always (the goal) to improve, to put a strong team because still it is pre-season.

“Of course this weekend starts the Premier League, but we still are in the pre-season. The boys are in a very good physical shape and they have to be used to playing twice a week. I don’t see that problem.”