Australia captain Ricky Ponting warned England on Friday they would be taking a gamble if they played a half-fit Andrew Flintoff in the Ashes series starting in Cardiff on July 8.
All-rounder Flintoff will miss the ICC World Twenty20 after surgery on a knee injury sustained in the Indian Premier League (IPL).
"That's going to be the great decision the England selectors are going to have to make come the first Test," Ponting told a news conference at Trent Bridge in Nottingham.
"Flintoff is obviously very important to their makeup and setup. Maybe, as we saw in 2007, if he's not 100 percent fit then maybe that sort of impact he can have around the team is not there.
"From 2005 to 2007 we saw two completely different players and that had a lot to do with the level of fitness that he had under his belt going into each series. That's where they're going to have a tough decision to make."
Flintoff was the outstanding player in England's 2005 Ashes triumph but failed to make the same impact as captain in the return series in Australia, won 5-0 by the home side.
Ponting, who opted out of the IPL to prepare for the Twenty20 World Cup and the Ashes defence, said the rest has done him good.
"For me it was pretty simple, it was about how long our summer was and how much cricket we played," he said.
"It was a good opportunity for me to have a couple of weeks off cricket and make sure that when I got here for the start of this tournament I was in the best physical and mental shape I could be."