"If it's given me something, it's giving me more and more support to my idea to be a manager," he says of his first senior management role as the club's 11-year stay in the Premier League teeters on the brink.

Is the pressure, stress and scrutiny worth it?

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"It's not the nicest," Selles, in charge until the end of the season, tells Sky Sports ahead of their Friday Night Football meeting with Arsenal. "Winning or losing, I've been in football long enough to know there are certain things you need [to deal with it].

"One is to keep your habits which move you through the motions and to make the result a little bit relative. Do what you can, control what you can, analyse what you need to do."

Winless in six games, four points adrift of safety with seven to play, Selles admits: "It has been desperate from the very first second. We are running out of time."

But this is what he expected. "To make the change from assistant manager to manager, whatever league it is, the challenge will always come from a situation that is not the best."

Defeats to relegation rivals West Ham and Crystal Palace in recent weeks has raised Opta's prediction to a 94 per cent chance Southampton will be playing in the Championship next season.

The 39-year-old Spaniard is largely blameless for the club's worst Premier League campaign in their history. Selles had "never an inch of doubt" about taking over from Nathan Jones in February and being the man who would potentially lead the club down.

His reign began with hope - two wins in three matches over Chelsea and Leicester - but their lack of firepower is just one major factor in their downfall.

"I would say that as a team we perform well in big parts of many games but the first goal goes against us and only against Tottenham we were able to come back," said Selles.

"If you take the first half of the game against Manchester City, the first part of the game against Crystal Palace, even against West Ham, you will see the pattern and what we need to do is be more robust and keep that performance for 90 minutes.

"We know we're a team that is not scoring a lot of goals so the defensive solidity is something we need to keep in every game."

It has been the biggest test of Selles' career which started as a fitness coach at Aris Thessaloniki and in Valencia's youth system and has been followed by various roles from assistant manager to performance analyst in Greece, Russia, Azerbaijan, Norway, Denmark, Spain and England.

Selles did not play professionally, instead he earned his UEFA Pro Licence aged just 25 and holds a degree in Physical Science and Sports. But nothing prepares you for a relegation scrap in the Premier League.

"One of the biggest things has been how to behave in the most complicated moments," said Selles. "When you are honest and always clear in your message you can navigate through almost anything. That's a big lesson, not that I didn't know it before, but it's at the most competitive level."

Does he take his new job home with him?

"It depends a lot on whether you feel comfortable with yourself. If the game has been a victory but a bad performance, in one way you lose," said Selles. "In your analysis, if you see a lot of things but it's getting the last bit of it then you're calm. That helps you arrive home and be a family man. Sometimes it's not possible."

The comfort blanket of being an assistant is long gone but Selles doesn't mind that. The youngest manager in the Premier League spoke privately with Roy Hodgson, the league's oldest, last weekend. "It was a very good experience for me," said Selles.

Whether he can match Hodgson's longevity in management will largely be down to where Southampton finish in six weeks' time. "The challenge for me is not just to be here right now but be here in 25 years."

And Selles isn't giving up yet.

Watch Arsenal vs Southampton live on Friday Night Football from 7pm; kick-off 8pm

Southampton's remaining fixtures

April 21: Arsenal (A) - Premier League, kick-off 8pm, live on Sky Sports

April 27: Bournemouth (H) - Premier League, kick-off 7.45pm

April 30: Newcastle (A) - Premier League, kick-off 2pm

May 8: Nottingham Forest (A) - Premier League, kick-off 8pm, live on Sky Sports

May 13: Fulham (H) - Premier League, kick-off 3pm

May 21: Brighton (A) - Premier League, kick-off 2pm

May 28: Liverpool (H) - Premier League, kick-off 4.30pm