Marcus North is refusing to take Andrew Flintoff lightly despite the all-rounder's less-than-impressive performance in the third Ashes Test.

Flintoff was not the same force with the ball in the drawn third Test at Edgbaston as he was when inspiring England to victory at Lord's.

There is concern there will not be sufficient time to patch up his knee problem in time to play in the fourth Test at Headingley which starts on Friday, and Australia captain Ricky Ponting has said the Lancastrian's fitness is visibly deteriorating.

But North, whose 96 helped Australia hold out for a draw in Birmingham, feels Flintoff will make an impact in Leeds.

North said: "You've got to be fair to Flintoff. His performance at Lord's was outstanding and one of the best bowling performances he has put in during his career.

"It is hard to be critical of how he has bowled in this game at Edgbaston. I think he has still applied pressure and bowled some pretty good spells.

"It is hard to compete with what he did at Lord's but he is England's 'go-to' bowler so I am sure he will be fronting up on Friday."

North also hit a century in the first Test at Cardiff and is determined to make it difficult for the Australian selectors to drop him if they feel the balance of the side needs altering.

He said: "It is up to Ricky (Ponting) and the rest of the selectors what balance the side will have.

"The beauty of the squad we have got here is that everyone, other than Brett Lee who was not fit, had a good case to fit into this Test line-up at Edgbaston.

"The most important thing for me is to try and perform as consistently as possible and make sure there is no room for any talk of leaving me out of the team so it was pleasing to follow up the first Test with a few runs here.

"I am always trying to work on consistency. I am pretty pleased with the way I've started Test cricket and hopefully I can build on what I have done so far."

Australia, meanwhile, are assessing their own potential injury doubt.

Vice-captain Michael Clarke has emerged as a worry for Headingley after developing an abdominal strain.

Clarke experienced discomfort after completing his undefeated century at Edgbaston on Tuesday and has since been diagnosed with a minor strain.

The 28-year-old batsman, whose knock in Birmingham was key to Australia saving the game, was withdrawn from a personal appearance in Leeds on Tuesday night and confined to the team hotel for treatment.

Australia physio Alex Kountouris said: "Michael Clarke has an abdominal strain that became sore after the completion of yesterday's game.

"He will continue to be treated with a view to him being fit for the fourth Test beginning on Friday."