England will be observing Welsh developments at fly-half closely after Paul Gustard revealed the Six Nations champions' defence must make adjustments according to who is selected.

Dan Biggar started Sunday's rout of Italy but departed at half-time after sustaining a blow to his ribs, presenting Sam Davies with the stage to orchestrate an impressive second half from Rob Howley's men.

Wales will name their team for the Cardiff showdown on Thursday and once it is known which playmaker will start, Gustard will modify England's defensive sights.

"Sam is a bit flatter to the line and he takes on the line a bit more. Biggar is a bit deeper back, but he has other strengths," Gustard said.

"It is not so much that we have to change defensively depending on their selection, but we have to have a heightened awareness of somebody.

"The kick and regather is definitely a strength of Dan Biggar's game, he is aerially very strong.

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"He's got a good cross-field kick as well and you saw a lot of that in the first half against Italy - and against South Africa as well.

"Davies comes to the line a bit flatter and tries to put balls across the face of defenders, so we just have to have an awareness about their individual skills.

"Whichever 10 they pick, Wales have a style of attack that they are developing. It is evolving and they are heading in a certain direction in terms of how they want to play.

"For us defensively, it may change a little bit with Sam, but fundamentally we need to get our things in order.

"We have discussed both 10s and how their likely traits might pan out, but we have also looked at some areas we want to work on from the France game and some key fundamentals that we need to get right."

George North suffered a dead leg against Italy and is also a doubt, but if passed fit Gustard insists the Northampton wing remains a major threat despite talk of his decline.

"I think teams may or may not put more numbers on him which would open up more opportunities," Gustard said.