Chelsea center-back criticizes squad for lacking fight and desire.
Billed as World Cup 2010 contenders ahead of the tournament, England now face an uphill task just to reach the last 16.
Terry is well aware the squad must improve if they are to reach the latter stages of the competition but is adamant there is still time to turn things around.
"The most frustrating thing for the manager [Fabio Capello] to see was the lack of fight and desire," Terry confessed to Sky Sports.
"We all, as a group of players, need to relax and do what we do week-in, week-out for our clubs and do what we did in the qualifying campaign.
"We shouldn't be changing the way we play and we shouldn't be worrying about other sides, because from what I've seen so far no teams worry me at all.
"Argentina are probably the best side so far. Everyone goes on about Germany and then they lose the game [against Serbia].
"We got criticised for playing a long ball game but, football-wise, we can mix it with anyone.
"I think everyone knows we can play. Week-in, week-out with our clubs we play football on the floor. But first and foremost, we're a proud country and we've got to go out there wanting to win."
Terry will be hoping to put things right on Wednesday, with Capello expected to make changes to his starting line-up, although the much-lauded centre-back stated the players still had the utmost confidence in the Italian's leadership.
"I have seen a few reports myself. There is no unrest in the camp at all," Terry reiterated to BBC Sport.
"I'm not going to sit here and question the manager. I'm here on behalf of all of the players to say we are fully behind him.
"Everyone is positive."
It remains to be seen whether England will be left to rue their poor performances against the USA and Algeria, when they face Slovenia in their must win encounter on Wednesday.
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