Flintoff has so far missed the opening two Tests of the four-match series against the West Indies, including England's innings and 283 run win here at Headingley on Monday, with discomfort in his left ankle, operated on twice over the last three years.
England coach Peter Moores, who has made it clear he wants Flintoff in the side only if the pace bowler can get through his fair share of overs, is looking to Lancashire's upcoming four-day county championship match against champions Sussex at Hove, starting on Wednesday, as the chance for the 29-year-old to prove his fitness ahead of the third Test which begins at Old Trafford on June 7.
But in a statement issued after a Headingley success which put England 1-0 up after the drawn opener at Lord's, the England and Wales Cricket Board (ECB) cast a shadow over Flintoff's participation against Sussex and, consequently, his chances of playing at Old Trafford.
The statement said: "Andrew Flintoff will continue to undergo rehabilitation and assessment on his injured left ankle and a final decision on his participation in Lancashire's county championship match against Sussex will be made prior to Wednesday."
Matthew Hoggard, whose groin injury sustained at Lord's opened the door for a spectacular England return by Ryan Sidebottom, who had match figures of eight for 86 at Headingley, also appears to be struggling to get fit in time for the third Test.
The ECB said the swing bowler would "continue to undergo rehabilitation and assessment on his injured groin and a decision on his participation in Yorkshire's upcoming county matches will be made in due course".
All of England's team at Headingley have been cleared for county action this weekend, including batsman Ian Bell who spent most of West Indies' second innings off the field with a back injury having suffered a spasm on Saturday.