England all-rounder Andrew Flintoff faces a race to prove his fitness for this summer's Ashes series after he was today ruled out of the ICC World Twenty20.

The 31-year-old was officially replaced in England's squad by Yorkshire leg-spinner Adil Rashid, who is yet to play a senior international game, due to Flintoff's failure to regain his fitness following a knee operation.

Flintoff had surgery following a slight tear to the meniscus in his right knee a month ago, which he sustained playing for Chennai Super Kings in the Indian Premier League, and was initially optimistic he could still feature in the tournament.

But despite making what an ECB statement describes as "an excellent recovery", Flintoff is not fit enough to play and will now continue his rehabilitation with Lancashire physio Dave Roberts as he attempts to return for the opening Ashes Test in Cardiff on July 8.

"Andrew is making excellent progress and there is no swelling or pain now in the knee," confirmed Nick Peirce, the England and Wales Cricket Board's chief medical officer.

"He has been putting in some extremely hard training with Lancashire and should start running and practising this week.

"After discussions with his surgeon we have decided that he should continue the remainder of his rehabilitation with physio Dave Roberts, who has overseen his previous rehabilitations."

Ironically, Flintoff's withdrawal from the World Twenty20 could help his build-up to the Ashes and he might play up to four championship games with Lancashire, fitness permitting, before the first Test.

His replacement in England's 15-man squad was more of a surprise with Yorkshire all-rounder Tim Bresnan, who played in the recent one-day series triumph over West Indies, expected to be given the call if Flintoff failed to recover.

Instead the selectors have called up 20-year-old Rashid, a talented middle-order batsman and leg-spinner, who was included on the winter tour to the Caribbean but failed to play an international match.

"We had to name Andrew in the ICC World Twenty20 15 because we hoped he would be fit but in reality the timescale was always optimistic," admitted National Selector Geoff Miller.

"There is a lot of cricket still to play this year and it is important Andrew is fully fit for it.

"It is an exciting opportunity for Adil, who was in the original 30 we named in early April. He has impressed the England management after being a part of the Test tour to India and the subsequent Caribbean tour and deserves his chance."