Harlequins face being in breach of European Shield rules for Sunday's all-English semi-final against Newcastle at Headingley.

Quins announced earlier this week that they might line up for arguably their biggest match of the season with three props and no front row cover unless Samoan hooker Tani Fuga shakes off an ankle injury.

European Shield organisers have rejected Quins' request to register an extra hooker for the match, leaving the London club short of numbers.

That prompted a threat by Harlequins' chief executive, Mark Evans, to withdraw his team.

But Quins appear to be in danger of breaching the Shield tournament rules, as published by European Rugby Cup Ltd, which state: "A club may nominate a maximum of 22 players and a minimum of 19 players for each match. Included amongst such players must be a minimum of five players who can play in front row forward positions and who are suitably trained and experienced."

The published rules do not state what happnes if a club arrives for a match without the full complement of five front row players.

Quins wanted to bring in under-21 hooker Johnny Roddham in the absence of Ireland star Keith Wood - out for at least three weeks with a rib injury - and the possible unavailability of Fuga, who is rated only a 50-50 chance to play.

But competition rules state that only players named in the original 30-strong squad submitted by clubs at the start of the tournament - plus two more nominated for the knock-out phase - are eligible to play.

Clubs also had a reserve list of four front row players, but Quins' two hookers from that quartet - Nigel Matthews and Matt Williams - have left the club.

Team manager Mike Scott called the rule ``ridiculous and unnecessary'' and added: ``Our request to have Johnny Roddham brought into the squad has been refused on the basis that it would be setting a precedent.

``Tani is a little bit more hopeful that he was at the weekend but if he does play there is every chance he will have to come off and we won't have a hooker on the bench so we will end up with uncontested scrums.

"Last Tuesday morning I had two fit international hookers and we never envisaged this problem occurring. Now we've lost two hookers in two games which a member of ERC earlier described to me as being `careless'.

"The medical team will work their hardest to see if they can get Tani fit to play. If not, we'll end up going out with three props in the front row."

Quins' three fit, registered props are Jason Leonard, Bruce Starr and Jon Dawson. Another prop, Simon Hackett, from the reserve list, is away serving with the Army, while back rower Andy Dawling, who could have played hooker, is suspended after being sent off playing for the Army. Hooker Ramin Mathieson - the other front row player in the original 30 - is also injured.

The prize for winning the Shield is entry into next season's lucrative Heineken Cup.

But Scott's stance was backed by Newcastle's director of rugby Rob Andrew, who said: ``I've been saying all season that I didn't really understand why we should have to name squads of 30 to be limited to this competition.

``If you have players registered to your club then it is down to you who you want to play in any competition.

"We've not been consulted on this and if we were we wouldn't have any problems with them playing Jonny Roddham at all.''

Newcastle have injury problems of their own with fly-half Jonny Wilkinson also a doubt with a neck injury.

"We'll see how Johnny goes for the rest of the week but we're pretty hopeful he'll be OK,'' Andrew added.

"He picked up another knock on Sunday but the cause of the problem was the London Irish game when he sustained what could be described as a whiplash injury.

"The Heineken Cup is a massive incentive for both of us. We've always taken the Shield seriously and we've enjoyed playing in it but this year there is an extra incentive."