THE threat Aberdeen pose to Celtic was visible even from 600 miles away.

Ronny Deila is still in the opening phase of his crash course in Scottish football but even the most cursory research into what he was letting himself in for, when he was first approached by Celtic in May, flagged up Aberdeen as their biggest immediate challenger. Between the start of the year and Deila's appointment Celtic played 21 games and lost only two of them. No prizes for guessing which team beat them twice.

Both losses hurt. The first, at Parkhead, put Celtic out of the Scottish Cup in February and the second, at Pittodrie 17 days later, was their first defeat in the league all season and the first league goal Fraser Forster conceded in 1256 minutes of play. Neither was of any consequence to Deila - they both came on Neil Lennon's watch - but they served to alert the Stromsgodset manager of the stiffest domestic challenger he could expect to face in his first year in Scotland.

Aberdeen did not finish second last season and are currently fifth - and Celtic third - but the widespread expectation is that the pair of them will be runners-up and champions respectively at the season's end. When it was put to Deila yesterday that Aberdeen at Pittodrie was the biggest test of his players' strength of character in the SPFL Premiership this season, he quickly agreed.

"I think so," he said. "It will be the toughest game and maybe the most 'fun' one as well. We are looking forward to that game. It is going to be a full house and I feel we are ready."

Last month Deila made a new signing. Or, more accurately, he moved a man who was working with the development players up to assist with the first team. Jim McGuinness gave up his work with the Donegal GAA team to spend more time with Celtic. Deila is a firm advocate of sports psychology and that's McGuinness's field of expertise.

"I have always believed in psychologists," Deila said. "Jim McGuiness is now working very closely with the players and he is a fantastically skilful man. I want him to get closer to the team because mentality and psychology is so important.

"Aberdeen away is a test of their mentality but his work with them is very early. The players have to be their own psychologists and I have to be a very good one. But it's important to have a team around you that gives you input and the chance to reflect on things. That's what we have - a big staff around the team - and that's going to help us win matches."

"The mentality of the team now is very strong. We are working really hard on that. I said on the very first day that we need 11 players who work defensively and offensively as well. On Thursday night [in the 1-1 draw against Astra in Romania] you saw that and that's why we are getting points away from home.

"We fight and we need to win challenges, but also we need skill to have a passing pattern and in the first half we showed we were dangerous and produced good moments. I think if we'd kept on going we'd have scored more goals. We have to learn from this and take the positives with us but also remember that is three times now we have gone up in games away from home in Europe and we have let the lead go."

Celtic were ahead against Legia Warsaw and lost, were ahead in Maribor and drew, were twice ahead at Red Bull Salzburg and drew 2-2, and were ahead on Thursday night before Astra equalised. Not once have they failed to win after taking the lead in a domestic match this season.

Charlie Mulgrew is fine for tomorrow's game despite receiving an horrendous challenge from Astra's Vincent Laban, who was sent off, while James Forrest has a chance of featuring for the first time in almost three months and Kris Commons could be involved after missing the last six games. John Guidetti, of course, will return after being ineligible for the European tie.