RONNY DEILA has held up Leigh Griffiths as a player with the level of professionalism he wants to see from all his men at Celtic.

Delia said Griffiths's ability with his left foot was "world class"and the best he had seen from any player in his life, but it was the occasionally controversial 24-year-old's attitude and determination to improve which has most impressed the Norwegian. As John Guidetti's goals have dried up, and Stefan Scepovic has yet to impress, Griffiths has taken over as centre forward in Celtic's past two matches. That has been a turnaround for a player who was rumoured to be on his way to Hibs on loan, or else heading out of Celtic altogether, during the January window.

When Deila questioned his players' fitness and diet in August he had looked for a reaction from Griffiths among others. "You learn when you are together with people that want to improve and make changes," said the manager. "These people always have a future. That's the culture I want. If that doesn't happen, the problem comes back to me and the whole club. Every day, I look to see if people are hungry to learn. Leigh has been a good example of that.

"The players have to understand what I am talking about. If you ask the best players in the world, you will find they are always humble and are always wanting to learn. They want to do it every day in training, you can see it in interviews and things."

In the close season Griffiths was due to face SFA charges of bringing the game into disrepute and acting against the best interests of football after he was filmed in a pub full of Hibs fans before an Edinburgh derby in April, when there were chants about Hearts going bust and former Hearts player Rudi Skacel being "a refugee". But the SFA's disciplinary hearing was postponed indefinitely until Police Scotland conclude their own investigation.

"Leigh has made improvements in a lot of things," said Deila. "I think he's a very exciting player. His left foot is world class. I've not seen any player have a better left foot in my life. He has skills but again you have to perform over time when you play at Celtic. I wouldn't play him if I wanted him to leave. We made some demands of him and he has really, really worked hard to tune into that. He still needs to improve, everybody does, but he is getting to a new level.

"Leigh is a fantastic guy. He is always in a good mood and you get a laugh in the dressing room. Also, his fitness is 100 percent better than it was and you can see that in matches. That's why he's got his chance, because he is doing a good job."

Deila has another full week to complete business in the transfer window. Celtic have yet to strengthen for the second half of the season and their only completed piece of business has been to sign Gary Mackay-Steven to join from Dundee United in the summer. The possibility of making a bid to buy out the remaining four months of Mackay-Steven's contract and sign him now is still being considered.

"These are very challenging weeks because you want to focus on football," said Deila. "There is so much uncertainty. You like a player, suddenly the player has to want to come then his club doesn't want to sell. There are so many different things when you start on a project, then it stops. It's a lot of work."