CELTIC'S concerns over the fitness of midfielder Stilian Petrov for tomorrow's UEFA Cup-tie with Blackburn were erased yesterday when the midfield man was declared fit, while on the other side of the city, Graeme Souness, the Rovers manager, was quite happy to put the finishing touches to his side's preparations at Murray Park. The former Rangers man-ager dismissed suggestions that he was winding Celtic up by using the Rangers training facility, saying: ''If we had been drawn against Rangers, I would have asked Celtic to use their training ground. But this is Glasgow and I shouldn't be surprised.'' Petrov, during a second consultation with a specialist in hand injuries, had it confirmed that he had chipped, rather than broken, the scaphoid bone in his right hand during Sunday's victory at East End Park and a solid cast would not be needed to protect against further damage. Instead, he will be able to wear a light support, cancelling out worries that the referee might decide that it would be too dangerous to allow him to play. Souness intends to monitor carefully how well his young players savour the ''unique'' Parkhead atmosphere but expects players like David Dunn, David Thompson, and Damien Duff will rise to the challenge. ''The atmosphere will be more hostile than anything these lads have experienced,'' he said. ''The more hostile it was, the more it turned me on as a player, and as manager I think I am still the same. I am going there with a young team who, although they have played at Old Trafford, Highbury and Anfield, will find the Parkhead atmosphere unique. ''I will tell my players to enjoy it. That is a mark of what you are. If you can go to places like that, if you have anything about you, the bigger the stage the better you perform. The more it turns you on, the more exciting it becomes. I will be looking closely at how they deal with it. But I expect them to handle it.'' His assistant, Tony Parkes, acknowledged that the build-up to this, the latest in the long- running Battle of Britain series, has been extraordinary. ''It's one of the biggest weeks in football I have experienced,'' he said. ''That was a fantastic result at Arsenal, but we have hardly had time to reflect on it before we're focusing on Celtic.'' Conviction will not be lacking in the Rovers camp, however much hype there is surrounding the tie. Said Parkes: ''Team spirit and confidence are high and we are all looking forward to it. I am sure they will want to prove a point or two and it will be a stiff test. But that's what we want, these are the kind of games you want to be playing.'' Whatever the outcome of the two-leg tie, Blackburn's all-time record goalscorer, Simon Garner, reckons Celtic fans should not be too concerned about the contract saga involving Martin O'Neill, even though O'Neill's BBC pundit colleague, Trevor Brooking, expects the Celtic manager to move to a big English Premiership club soon. Garner played under O'Neill at Wycombe Wanderers and he insists that O'Neill's methods have always been unorthodox. ''He has never gone through a bad patch as a manager, and you can see why clubs in England would want him. ''You can never tell what Martin is going to do, but I do know that once his mind is made up he sticks to it. He is a very loyal man. He doesn't worry about pieces of paper, as I found out when he signed me. I heard 10 weeks before I signed that he wanted me and I was always ringing him up asking when it was going to be done. He wasn't bothered as he knew he would get me. He just told me it would all work out in the end, and it did. So I don't think the Celtic fans should be too concerned as I know he is happy there and at whatever club he's at he puts in 110%.'' Garner hit a record 168 league goals for Rovers in between being signed by Jim Smith as a teenager in 1978 and being sold on by Kenny Dalglish in 1992. ''I had eight months under Kenny Dalglish and he was always very calm.'' he said, '' He would sit in the directors box or if he was on the touchline wouldn't say anything during the game. Martin, on the other hand, never keeps still and was always egging us on from the touchline, especially if we were having a bad game. He's always been the great enthusiast and I imagine the 60,000 at Celtic love that.'' Unsurprisingly, Garner reckons Souness' team will come out on top. He said: ''It's a hard one to call but I think that over the two legs Blackburn will just edge it. The whole side is playing well at the moment and I'm sure it's going to be a great game.''