Andrew Flintoff is expected to be given until Friday night before England decides on his fitness for the fourth Ashes Test.
All-rounder Flintoff batted in the middle at Headingley on Wednesday but opted not to bowl as a precautionary measure.
The 31-year-old has been icing his injured right knee since the Edgbaston draw on Monday night, which left England 1-0 up with two to play.
He did not bowl in that match once it became obvious England could not win and the management are likely to put off any decision until right before the match.
Flintoff has so far defied the pain to turn in a man-of-the-match display with the ball at Lord's and returned to form with the bat with 74 in England's only innings in Birmingham.
Fast bowler Graham Onions said: "Everyone knows that Andrew Flintoff is a legend who is a great person to have in our team. I think we are a stronger team with him but that is only if he is 100 percent fit."
"Andrew's going to be very honest. It is a shame that his body is in a little bit of discomfort at the moment but I am sure he will do everything he possibly can to be fit."
England's attack has offered a collective menace throughout the series when the ball has swung but has been less effective when the sun is out and the track is flat.
Flintoff's aggression generally takes the effect of the conditions out of the equation, however, and they tend to change with the weather in Leeds - cloud cover usually brings wickets and sunshine runs.
"When the ball swings it is a massive bonus and it is a great thing to have as a bowler," said Onions. "If you just bowl straight against great players you know they'll score a lot of runs."
"For us as England cricketers, we need to make sure the ball swings or does something off the straight, or be aggressive. We've got a few plans that we need to bowl to."
"But we've still got the belief we can beat Australia without the ball swinging and we were close to winning the last Test."
"We put ourselves in a strong position and, although it didn't happen, we took a lot of confidence from that and we're looking forward to this Test believing we can win."
England can complete successive home Ashes series wins in the coming week and can expect support, even if somewhat more restrained than usual, from the notorious Headingley crowd.
Australia captain Ricky Ponting has been booed throughout the series but the authorities have appealed for more respect to be shown and Yorkshire have put measures in place to counter drunken behaviour around the ground.
"I think us as players, it's important that we don't listen to too much of what goes on," said Onions. "Inside the rope, it's just action, everything is happening so quickly."
"I still class Ricky Ponting as one of the best batsmen in the world, if not the best. Myself I would never boo him because I have too much respect for him. Whatever happens off the field, away from the white lines, that's out of my hands."