Aussie giant Graham Mackay joined the Bulls in their "strictly private" Challenge Cup preparations at Odsal yesterday but he'll be heading for Henley not Twickenham on Saturday.

The powerhouse three-quarter agreed a short term deal with the Bulls in time to be placed on the cup register but contractual commitments with Leeds Tykes mean he is not available for the rugby league showpiece against St Helens.

The Bulls had made a move to bring forward his switch to league after backs Stuart Spruce, Shane Rigon and Lee Gilmour all suffered injuries at Hull on Saturday and the Tykes clinched promotion to the Zurich Premiership.

But Bulls coach Brian Noble explained: "Graham's arrangement with Leeds means that he must play against Henley on Saturday to fulfil his contract and receive what financial rewards are due to him and unless that situation changes he will not be available for us.

"He may have come into contention otherwise, especially if the injury position does not clear-up as we would hope."

"Having said that, Graham will definitely be available for the Warrington game next Wednesday and the time he spent with us yesterday was useful in preparing him for that."

Better news for the Bulls today was that winger Tevita Vaikona was running flat out at training yesterday after recent ankle trouble which saw him rested at the Boulevard on Saturday.

Rigon (knee) and Gilmour (head knock) also proved their fitness but major concerns remain over full-back Spruce and utility back Michael Withers.

"Scans have showed that there is no major structural damage to Stuart's shoulder but it is not improving at the rate we would have hoped," said Noble.

"It will be a blow if he is out because his experience is invaluable but he is still hopeful and we will see how things look over the next 24 hours.

"We also have to discuss the situation with Mick. His hand is healing but we have to consider what the risk is of further damage."

Noble and his 19-man squad were heading for their training camp in Slough this afternoon and the players will be told of his final selection tomorrow morning although he is unlikely to make it public until just before kick-off on Saturday.

Meanwhile Saints coach Ian Millward insists the prospect of clinching a unique treble of world club champions, Super League champions and Challenge Cup winners is not weighing them down in the build-up to the game.

"There is absolutely no pressure on us," he said. "If we do win on Saturday it won't mean that we're the best team in 100 years but we will be ranked up there with the best."

Bulls: (from) Spruce, Vaikona, Withers, Naylor, Rigon, Pryce, Gilmour, H Paul, R Paul, Deacon, Vagana, Lowes, Anderson, Fielden, McDermott, Gartner, Peacock, Forshaw, Radford.