The Rugby Football League are to tighten the rules on eligibility after Hull avoided being thrown out of the Carnegie Challenge Cup on a technicality.

Prop forward Jamie Thackray, who joined Hull for a second time from Leeds on March 27 - more than three weeks after the initial cup deadline - played in both the next two rounds but the matter only came to light after his side's 32-18 win over Widnes last Sunday.

The RFL's board of directors, who spent most of yesterday considering the issue, claim they regard the breach as a "very serious matter" but stopped short of throwing Hull out of the competition because it is not in the rules.

Instead, they have ruled that the results so far will stand and that the quarter-final between Bradford and Hull at the Grattan Stadium, Odsal, will go ahead.

But they have also asked the RFL's compliance manager Karen Moorhouse to investigate further and decide what punishment to impose and Hull are likely to be handed a heavy fine.

A statement said: "The RFL board intend to review the operational rules relating to competitions and will consider whether the rules should be amended so that offences of this nature will lead to mandatory expulsion from the cup in future seasons."

The confusion arose because of the decision of the RFL to introduce a second deadline to register players for the Challenge Cup following the switch of the competition to later in the season three years ago.

Players must be registered by Monday of the week leading up to the third round to be eligible to play in the next three rounds, while players signed up to the Monday before the quarter-final stage are free to play in the rest of the competition.

Widnes had agreed beforehand to adhere to the outcome so there is not expected to be any further threat to the tie, which will be shown live by the BBC.

The date for the match has not yet been agreed because of ongoing difficulties in finalising the arrangements for the quarter-final between Leeds and Wigan, which has also been selected for live broadcast by the BBC.

The tie clashes with the Roses county championship cricket match at Headingley and Leeds are hoping to negotiate a compromise with Yorkshire to avoid having to look for an alternative venue.

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