England captain Matt Dawson is struggling to make Northampton's Tetley's Bitter Cup semi-final appointment with London Irish at Reading on Saturday.

Dawson suffered a rib injury during England's 19-13 Six Nations Championship defeat by Scotland on Sunday, and is thought to have little chance of lining up at the Madejski Stadium.

Dawson has been named in Saints' 25-man squad along with two other scrum-halves, Dom Malone and James Bramhall.

Malone is the favourite to step in if Dawson is ruled out, but an injury to arguably their most influential player is the last thing Treble-chasing Northampton need.

Starting on Saturday, they enter a critical phase of their season. After London Irish, Saints face Wasps in the Heineken Cup quarter-finals, followed by Premiership clashes in quick succession against Harlequins, Bath and Leicester.

"The worst scenario is that Matt would be out for a month," said Northampton rugby director John Steele.

"This side is not reliant on any one player but, having said that, he is a world-class player and it is very difficult to fill his shoes."

Dawson sustained the injury during England's Calcutta Cup demise, and at one stage it looked as if he might go off as his scrum-half replacement Andy Gomarsall had stripped off his tracksuit and looked ready to replace him.

But Dawson played on, doing his utmost to rescue England from an increasingly desperate position, a task that ultimately proved beyond him.

He is having continued treatment for the injury but, England's skipper apart, Northampton have a clean bill of health as they bid to reach Twickenham for the first time since 1991.