The Three Lions skipper was injured during a training session ahead of Saturday's clash with the South Americans.
If Terry does miss out, the captain's armband could go to Wayne Rooney given the number of senior players sidelined.
Big blow: John Terry (right) is the latest England player to be injured
Chelsea defender Terry suffered a swollen achilles blocking a shot from Jermaine Jenas during their preparations in Qatar.
The 28-year-old defender was due speak at a press conference in the Ritz CarltonHotel on Friday but did not emerge, with Gareth Barry taking his place instead.
Capello remains hopeful that Terry will be available but it is understood that is overly-optimistic.
Double trouble: Terry (left) is set to join Frank Lampard on the sidelines
'He has hurt his ankle and we need to check him but I think he will be okay,' said the Italian.
Although England's medical team are yet to make a final decision onTerry, he is almost certainly out of the friendly in Doha. The bruisingis unlikely to subside over the weekend.
Contender: Wayne Rooney
It is the latest blow for England, who are already without key menFrank Lampard, Rio Ferdinand, David Beckham, Steven Gerrard, GlenJohnson, Ashley Cole, Emile Heskey, Carlton Cole and David James forthe glamour friendly in the Middle East.
Lampard flew home on Thursday after suffering a thigh injury in training.
A number of key players were unavailable to Capello despite the prestige of playing the Brazilians.
Manchester United striker Rooney is behind Terry, Ferdinand, Gerrardand Lampard in the pecking order but he may now become skipper bydefault.
However, Capello may decide that Manchester City midfielder Barry is a safer bet.
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