"Flintoff reported some discomfort in his left ankle following the County Championship match between Lancashire and Hampshire on Saturday," the ECB said in a statement.
"He has undergone a scan and the results will be reviewed later today. A further re-assessment of Andrew's injury will be made by the ECB Medical Team tomorrow morning prior to the England team's net practice at Lord's."
Flintoff missed much of last season with ankle trouble and has twice undergone surgery.
England are already without captain Michael Vaughan for the first Test of the four-match series, with opener Andrew Strauss taking over the captaincy instead of Flintoff, who was skipper for the 5-0 Ashes whitewash defeat in Australia.