Flintoff was included in a 14-man squad named on Monday -- with pace bowler Steve Harmison the only addition -- but the England and Wales Cricket Board said in a statement the all-rounder's place would depend on the results of a scan.
"We have a like-for-like selection with Steve Harmison coming into the squad from a bowling point of view," England selector Geoff Miller told Sky Sports News.
"But we will need to consider all our options carefully when we come to determine the make-up of our bowling attack at Lord's and the final decision will depend on our assessment of the pitch and the likely overhead conditions," Miller added in the ECB statement.
Harmison won his recall following a series of good performances for Durham.
Flintoff scored 37 in the first innings in Cardiff and made a big contribution to England saving the match with 26 in the second. He took one wicket at a cost of 128 runs.
He had surgery on the knee earlier this year after injuring it playing in the Indian Premier League.
Seamer Graham Onions and batsman Ian Bell, who were named in the squad for Cardiff but did not play, retain their places.
