England scrum-half Matt Dawson could be sidelined for six weeks after suffering a knee injury during Northampton's Zurich Premiership victory over champions Leicester.

Dawson, who won his 47th cap in England's record 53-3 success against South Africa 11 days ago, enjoyed an outstanding autumn Test series.

But he lasted just 10 minutes last Saturday before being carried off in Saints' memorable win at Welford Road, which ended Leicester's 57-game unbeaten home league record.

Northampton report 30-year-old Dawson faces a possible six-week lay-off.

If initial forecasts prove accurate he will miss Northampton's back-to-back Heineken Cup appointments with Cardiff, a Powergen Cup sixth-round tie at Orrell, plus Premiership games against Gloucester and London Irish.

Ideally, Saints would want him back for a crucial Heineken Cup clash against Biarritz on the weekend of January 11/12. But Dawson's England prospects should not be affected, given that their Six Nations opener against France is not until February 15.

Dawson's place for the Franklin's Gardens showdown with Cardiff on Saturday goes to Ian Vass, who took over from him at Leicester and scored a try.

Saints coach Wayne Smith has made changes elsewhere in the side, handing England squad member Robbie Morris a start instead of Lions prop Tom Smith, while Wales lock Steve Williams returns after recovering from illness.

Williams, laid low by a virus last month, will pack down alongside second-row partner Rob Hunter against his former club.

Behind the scrum, wing Jon Sleightholme takes over from New Zealander Bruce Reihana who is not eligible for the Heineken Cup group stage.