Of all the phone calls Ronald Koeman must have made this summer, few could have been as important as the one he placed to Madrid in late August.

With the transfer deadline approaching, Saints had set about trying to elevate their squad by securing a couple of significant late additions.

One name that had appeared on the radar had been that of Toby Alderweireld, the Belgian international defender.

Saints had become aware that he could be available on a loan deal from Spanish champions Atletico Madrid, but signing him would not be simple.

The 25-year-old boasted a seriously impressive pedigree, was coming off a fine World Cup and there was stiff competition for his services from across Europe.

Yet it was Koeman, left, who played the most pivotal of roles in Alderweireld’s decision to dismiss those other offers and instead join Saints.

“The most important thing was the coach,” said Alderweireld.

“He called me and said ‘We really want you’ and, for me, for one year, that was the most important thing, that I get the confidence from him and to play football.

“He called me when I was in Madrid. We had a good conversation, and he said ‘Yeah, no problem, if you want to join us we will be taking you’, so for me it was very good. Footballers need confidence. That’s the most important thing – and that’s what he gave me.”

Alderweireld added: “Of course, some people asked me before: ‘Is Southampton the right decision?’ Now they say ‘Yeah, good decision!’”

Another decision might await next summer for Alderweireld, who, as part of what is currently England’s best defence, has helped guide Saints to second place in the Premier League table.

His loan deal at St Mary’s will expire at the end of the season, and, although Saints are understood to have the first option to sign him, he says it is up to Atletico to first decide if he can go on a permanent basis.

“I know Atletico decides, and that’s normal,” explained Alderweireld.

“Then, of course, Southampton can have a say, and, at the end, it’s my choice of course.

“But I promised to Southampton to give my 100 per cent this year, no matter what, so I will do that this season, and I will help the team, and then we have time enough to see where my future will be.

“I can’t say anything about it, because I don’t decide.

“Of course, I have my thoughts in it, but Atletico owns me, so it’s not up to me.”

Yet, right now, there is nothing to suggest that he wouldn’t be happy to stay.

“For sure, I’m really happy, I’m really enjoying Southampton,” said Alderweireld, who is living in the city with his girlfriend.

“They are very professional, they are going to the top with their own philosophy.

“The new complex is there, the training facilities, so they are building on their way and it’s really nice to be there and be a part of that.

“I will do my best and next year we will see.”

So far, Alderweireld’s best has been pretty darn impressive.

That is perhaps no surprise, given what he has already achieved at such an early stage of his career.

“Yeah, I’m four times champion – three times in Holland, one in Spain, played in final of Champions League, World Cup quarter-final, so I want to bring it to the other guys,” he said.

“Not to say ‘do this’ but just talk about football and my opinion about it. That’s the way I want to play.

“Because of Holland, I was 19 and you can play a lot. That’s the positive side of Holland.

“Then, in Madrid, it’s hard, it’s hard. It’s really professional, it’s more men football, you know, and I really learned to defend well.

“So, with the football from Ajax, and the defending of Atletico, it was the right step.”

While leaving Madrid might not have been a simple decision, Alderweireld was confident enough that it was the correct move for his own sake.

He said: “I played in all the competitions, 25 games. It’s not nothing, but I wanted to play more.

“I’m a real football player, I really like to play. Nobody likes to be on the bench.

“But, like I said, I learned a lot defensively and I won the league in Spain, and played in the final of a Champions League, so it was a great experience.

“Now I wanted to play more, weekly, and show myself.

“In games I played well, I trained well, but the coach had no reason to change, and I understand that, and that’s why I wanted to play here.”

Saints are certainly glad that he did.

So too, no doubt, is team captain Jose Fonte, who has formed a wonderful partnership with Alderweireld in central defence.

“It feels very good,” said Alderweireld, of their combination.

“From day one, it is going very well, but I don’t like to say defensively it is only our two, because Clyney (Nathaniel Clyne) is helping, Ryan [Bertrand] is helping, and it feels like when somebody drops, the other one takes it.

“Someone makes a fault, the other one makes it good for you.

“That’s a good feeling, it’s important to have the confidence, that you can make a mistake, but the other one is helping you, and that gives me a lot of confidence to play.”

While many people are already focusing on the run of fixtures Saints face beginning this Sunday with Manchester City at home, Alderweireld insists no one at St Mary’s is looking beyond tonight’s trip to Aston Villa.

“Some people are thinking about next month,” he said. “We are just focusing on Villa.

“Nobody in the squad is talking about anything else.

“Monday is going to be very tough, very difficult, and we are looking at how we can beat them.

“We can have three points there, and that’s important.”