RONNY DEILA faces some serious tests of his powers of persuasion as several of his players prepare to decide where their future lies.

The Celtic manager has made it clear he wants to retain Bhoys such as Jason Denayer and John Guidetti when their loan deals end.

Deila is also eager to have Virgil van Dijk ignore overtures from clubs down south, and further afield, and remain at Parkhead for at least one more season.

With the re-constituted Nir Bitton also attracting interest from clubs with money-aplenty to splash, the opening of the summer transfer window threatens to be an anxious time for the man trying to build a team, not dismantle one.

This week, he sanctioned Liam Henderson's three-month loan deal to Rosenborg in an attempt to accelerate the 18 year-old's development.

But, Deila wants to hold onto his best stars.

At the same time, the Norwegian acknowledges and respects ambition, and has the benefit of being able to bring genuine empathy to the table when he sits down his players.

The 39 year-old openly admits he harbours serious regrets about his own career, in particular, opportunities which he did not pursue.

He stayed with Odd Grenland for 12 years, winning only one cup, before, aged 29, finally cutting loose and joining Viking Stavanger.

It's very much a case of if-I-knew-then-what-I-know-now for Deila, who, if he had the chance to do it all again, would choose a very different career strategy.

Asked by Celtic TV what advice he would give to a young self, he answered: "Be disciplined.

"If I'd been more disciplined when I was young, I would have become a much better football player.

"I think I was too much enjoying life. That's important.

"But, I didn't get coached in the way I should have. It was not that way at that time.

"I worked hard, but I could have done better things, and I could have been pushed more.

"I would also take more chances.

"I was in the same club for 12 years. I should have left earlier to get bigger challenges, like I have done as a coach.

"That would also have made me a better player.

"So, I think that's the two things, more discipline and go for more challenges."

Deila certainly took on a huge challenge when he moved from his comfort zone at Stromsgodset to succeed Neil Lennon at Celtic Park.

Nine months later, he has emerged from a very tricky opening period to stand on the threshold of bringing the first Treble to the club since 2001.

The consistency which was lacking at the start of the season has now been harnessed, though defeats like the one to St Johnstone last month are constant reminders they are not yet immune to a shock to the system.

Ironically, the more successful his players are this season, the more attention they will attract.

That, in turn, could mean Deila has another major rebuilding job to do this summer.

While he accepts developing young players to sell them on for big profit is part of the club's financial strategy, Deila would like the chance to get the this group up to the level he wants them before he has to say goodbye to some of his key performers.

Bitton is a case in point.

Pparallels can be drawn between his own unfulfilled early career and where Bitton was headed.

He had been a slow burner since his arrival from FC Ashdod in 2013.

Having worked hard to make him conform to what is required to be a first-pick, and watching him then blossom into a major figure in the team, the Israeli international's ability is now being recognised by scouts who were perhaps taking in a Celtic match to watch some of Bitton's higher-profile team-mates.

Deila takes great pride in helping the midfielder - who managed to play 90 minutes for his country against Belgium on Tuesday, despite requiring x-rays on an ankle injury he aggravated while playing against Wales at the weekend - realise his potential.

He explained: "Somebody finds the key to development. We had a hard fight in the beginning of the season to understand what that means.

"I couldn't see how we were going to use him if he didn't get more intensity in what he did. And that starts in training.

"We had a very good talk, and he has really, really put the effort in that he needed.

"You can see what he gets out of his talent now, and this is just the start.

"He is the role model for what can happen with a player if you work in the right direction."

High praise, indeed, for someone who, only a few months ago, looked destined to spend his Celtic career on the periphery of the team.

Bitton admits he was falling into the trap of simply blaming the manager for not recognising what he had to offer.

Deila is delighted the penny finally dropped with a young man who is now being likened - albeit undeservedly - to Yaya Toure.

"I don't think he was conscious of what really goes into it," said the manager.

"Everybody has to stop finding excuses. There is always a reason why you don't play.

"If you put everything on the coach, then you are lost. You are finished.

"You have to go into yourself and ask. 'Why am I not playing? Why is that guy in front of me?'

"When you find that out, you have to think. 'Okay, what do I do to get better?'

"That's what he has done, and now he's taking steps all the time and he gets his chances.

"You have to show in training you are good enough, then you get your chance. He has done that."