WEST of Scotland hooker Carlo di Ciacca will make his debut for the Glasgow Caley Reds in tomorrow's vital European Cup encounter with Pau.

The 22-year-old's call-up to the starting XV came after Gavin Scott was declared unfit to play yesterday, suffering from a bruised thigh. Scott himself was in for captain Gordon Bulloch, who was concussed in last weekend's defeat by Leicester Tigers.

Di Ciacca's elevation means that Kirkcaldy and Scotland under-21 prop Andrew Welsh is recruited to the bench. Should any misfortune befall the debutant during the game, Gordon McIlwham will move from prop to hooker.

Coach Richie Dixon explained the late decision to rest Scott last night. ''Gavin had a slight injury to his shoulder and a knock to his thigh after last week's match,'' he said.

''The shoulder is fine but his thigh, having initially responded to treatment, did not heal quickly enough. Unfortunately, he would not have been in a position to be able to take contact, although he can run.''

As for di Ciacca, Dixon was happy that the youngster would perform. ''Carlo has trained with us before, and has been with us all week,'' he said, ''so we are happy that he knows all the relevant moves and lineout codes.''

Rugby globetrotter James McLaren, meanwhile, is convinced that the Reds can come back from the dead to reach the knock-out stages of the European Cup - as long as they believe in their own talents and worry less about what their group rivals may or may not do.

Former Stirling County and Bourgoin-Jallieu man McLaren has been sidelined since Scotland's tour of New Zealand with an ankle injury, but now he is determined to make up for lost time by playing a major part in a Cup revival in the wake of their defeats by Pontypridd and Leicester.

''It has been frustrating for me,'' he admitted. ''I had been on a real high on the tour - but that is typical of rugby these days, swings here and roundabouts there.''

McLaren came face to face with Pau on several occasions during his sojourn in France, and he believes the Reds have the firepower to not only sweep them aside at Hughenden, but also go on to complete the double next weekend.

He told how he and the other player in the squad with prolonged French experience, Mark McKenzie, had only given a brief lowdown to their squad-mates on the qualities and shortcomings of Pau.

''You can easily fall into the trap of talkking about the opposition too much at the expense of talking up your own side's abilities,'' he insisted. ''I told the lads that what stuck in my mind about them was their liking for rolling mauls, particularly from line-outs.

''In stand-off David Aucagne, they also have a man who can move the ball wide at a pretty slick rate.''

McLaren proved his fitness with two outings on the wing for County against Peebles and Biggar. He said: ''I am delighted to be making my debut for Caley from the start of the match rather than coming on from the bench and trying to catch up with the tempo of play.

''I know that my chance has come through Ian Jardine's injury - and I am also aware that if I don't produce the goods right away, Jardy will be hammering on the door.''

On his prospects of an immediate Scotland squad recall for next month's Murrayfield Tests against Australia, Samoa, and USA, McLaren stated: ''I don't intend to rush things. My goal is to earn a regular place in the Caley line-up.''

McKenzie, meanwhile, also couldn't disguise his delight at being back in the Reds' starting formation after losing his berth to Tommy Hayes for the past month. but he was quick to declare: ''It is good to have competition in the team.

Tommy is a first-rate player and he played brilliantly in the victory over Cardiff, so it would have been unjust to have dropped him.''

Like McLaren, he is upbeat about Caley's prospects of launching a successful European salvage mission. ''If we can get ahead early, we should be able to put quite a few past them and that would set us up nicely for the return trip,'' he said.

''There is no reason why we can't beat them twice. Conditions over there will be perfect. It might not be that warm because Pau is at the foot of the mountains, but it should be sunny. There will also be a great atmosphere with 10,000 of them, all chanting away every minute of the game.

McKenzie admitted he was looking forward to measuring himself against Aucagne, saying: ''I don't regard him as a great threat in attack running-wise, but tactically he is very astute. He knows when to kick and when to pass and has a good pair of hands. They play round him - he is their main man.

''The big danger is when he fires out big long spin passes to the guys on the wings.''

McKenzie also picked out ubiquitous winger Pascal Bomati as a potential danger. He said: ''He is a fast and powerful wee redhead who has played for France at every code of rugby - sevens, union and league.''

The stand-off also stressed that patience would be the watchword for the Reds tomorrow. ''We definitely tried to rush things against Leicester last week. European rugby is exactly the same as European football - you don't try to score every time you get the ball.

''Sometimes you have to take the easy option by going into contact and laying the ball back, rather than trying to make the extra yard and end up losing possession.''

The French side will be without influential Canadian Test skipper Al Charron, who was injured shortly after the interval against Pontypridd. He is replaced by seasoned campaigner Thierry Cleda, who also has plenty of international experience. Teams:

Glasgow Caley Reds - R Shepherd; J Steel, A Bulloch, J McLaren, G Metcalfe; M McKenzie, G Beveridge; D Hilton, C DiCiacca, G McIlwham, S Campbell, S Griffiths, J White, G Simpson, J Petrie. Replacements: A Welsh, A Watt, D Burns, M Waite, F Stott, T Hayes, S Longstaff.

Pau - D Traille; P Bomati, S Guilhem, J-C Cistacq, X Cambres; D Aucagne, P Carbonneau; M Larrouy, M Dal Maso, S Bria, T Cleda, A Lagouarole, Abder Agueb, L Maillier, E Gouloumet. Replacements: P Etchegaray, J Rey, N Bacque, G Combes, B Aurignac, L Arbo, D Arrieta.