The 35-year-old, soon to be returning to the Lane, marked his 41st international appearance by scoring a stunning second half free-kick in England's 4-0 warm-up win over Mexico at Pride Park.
Teddy suspects the morale of the whole group has been lifted by acquiring a winning habit of late — four straight wins under coach Sven Goran Eriksson.
"The new manager has come in and we've had a lot of good results and everybody is playing with a lot of confidence," said Teddy.
"I think you've got to hand a lot of respect to the manager for coming in and giving people that freedom to play and it's certainly shown in the four games we've had.
"The relaxed mood comes from winning games. We've won the last four, so everyone is relaxed even though we are aware Wednesday's game is massive and we need a win.
"It's a massive challenge for us, but we know what we are good at, at the moment, and the first half hour against Mexico was the best we've seen England play for a good number of years.
"You know if you can play like that, then you hope that you can play like that again. Things seem to have clicked into place. It won't be quite the same sort of game as Mexico and the Greeks will be home with a hostile crowd behind them, but we know what we can do so that gives you a lot of optimism."
Teddy went on to describe the boost that his strike against Mexico has given him — a welcome one given the competition he faces at international level.
"I think it is always important to score and always important to play well, especially when you are playing for England because you sometimes don't get another chance for three or four months.
"There is a lot of talk about who wants to play and who's going to play and if you don't perform well you're easily dismissed at this level. I would have enjoyed scoring a goal like the one against Mexico at any stage of my career. To do that for England is a wonderful moment.
"The older you get the less chance you think you're going to have to be involved in a team like this, so I suppose you cherish it a little bit more."
Teddy Sheringham believes the England squad are in the perfect frame of mind to tackle the challenge of securing three points against Greece in Athens.