RONNY Deila today insisted that Leigh Griffiths does have a long-term future under him at Celtic - if the striker can increase his fitness levels.

Scotland internationalist Griffiths has only been used sparingly by Deila since he took over as manager at Parkhead this summer.

The 24-year-old forward has only made three starts in the Hoops' 14 competitive games in the 2014/15 campaign and has scored just one goal.

His Norwegian boss insisted that Griffiths remains part of his plans - and could feature against Dinamo Zagreb in the Europa League tonight.

But Deila has told the player he has to buy into the strict diet and fitness regime he has introduced on the first-team squad at Celtic.

The Hoops gaffer explained: "Griffiths can be part of the game against Zagreb. He's in the squad, so we'll see.

"I talk to my players about what they have to improve on or not. He knows exactly what those things are and he really wants to improve as well.

"First of all, Leigh has to increase his fitness. That is his first task. That's something he is aware of.

"We have good processes going on with that. Leigh is a good football player and he scores goals.

"But I know he can be much sharper and stay on top of his game for 90 minutes.

"Once he has that then he will be so much better."

Since falling out of the first- team picture at Celtic Griffiths has been linked recently with a return to his former club Hibs, who tried and failed to get him on an emergency loan deal.

But Deila insists there is no chance of the hitman going out on loan or being sold.

The former Stromsgodset boss said: "Leigh is going to stay here, so there is nothing more to talk about.

"He has told me he wants to stay. We need him and we have a lot of games coming up. So that's how it's going to be."

Meanwhile, Deila has urged Celtic supporters to be patient with Serbian striker Stefan Scepovic and give him time to adapt to Scottish football.

The £2.3million acquisition has failed to hit the target in five first-team appearances.

And he drew a blank against Salzburg in the Europa League a fortnight ago.

However, his manager is still convinced that the man he landed from Sporting Gijon in Spain will be get his name on the scoresheet before long.

DEILA explained: "It is very important now that the new players adapt to the Scottish way of playing.

"John Guidetti has played in England with Manchester City, so he knows more about the game here.

"But if you look at other leagues around the world you can see that that players often take time to settle.

"The Brazilian Neymar, for example, took his time before he did well with Barcelona.

"It will take the players time. It is the same as me coming in here as a coach. I didn't know everything about Scotland.

"The new players have to settle down and start working with their team-mates. Then things will happen."

Scepovic appeared to shy away from the physical aspect of the game against Salzburg over in Austria.

But Deila revealed he had spoken to the player about the importance of him imposing himself on defenders.

The Celtic boss said: "Stefan knows everything about this. I talk to my players all the time.

"We look at what is positive and also what are the negative aspects after every game.

"Stefan is a very clever boy. He knows he has to adapt to that kind of play.

"But I think that the level of the Second Division in Spain, where he played last season, is at least as high as it is here in Scotland."

Scepovic notched 23 goals in 41 games for Sporting Gijon last term and Deila added: "He knows that he can score goals. I see his movement and I know goals will come.

"But he has come to a new country, to a team with new players, he hasn't played in a long while and there are big expectations on him.

"We just have to be a little bit patient with him."

Deila endured a difficult start as Celtic manager as he watched his team lose twice in the Champions League qualifiers, first to Poles Legia Warsaw and then, after they had been reinstated, to NK Maribor.

SINCE that shattering home defeat at the hands of the Slovenians the Scottish champions have been unbeaten in their last six matches.

And they have won their last two competitive outings against Hearts in the League Cup last midweek and St Mirren in the Premiership on Saturday.

Now Deila is confident his team can build on the progress they have made in recent weeks by overcoming Croatian rivals Dinamo Zagreb this evening.

He said: "I knew it was going to be difficult at first. It is very tough to get results while at the same time also bring improvement to the team.

"Doing things the right way while results are not good can be very difficult. But you have to stay with what you believe.

"However, I think we are now going forward. We are working well in training and we've had some good spells in matches.

"We are still in every competition we want to be involved in.

"The process from now on is going to be very important.

"It's about development and winning trophies. That's what we're going to talk about.

"You can push me as much as you want but I believe in what I'm doing and where we are going. We will see in the end."