Jagielka was ruled out for two months towards the end of the season with a hamstring injury but has made a return to action at just the right time.
The Everton defender benefited from the training camp in Portugal last week and is now working to ensure he will be ready for the opener against Italy.
"People may be playing down our chances but momentum is a fantastic thing in football."
Phil Jagielka
With England facing a friendly against Peru on Friday night at Wembley and then two more warm-up fixtures against Ecuador and Honduras in Miami, Jagielka knows he will have plenty of time to get crucial game-time before the first group match in Manaus on 14 June.
Speaking at their St. George's Park base, Jagielka said: "It was an important week last week, getting out to Portugal to get a few more sessions under my belt, and we had a really good session today.
"I do not need to be 100 per cent fit this week, it is more about building up and getting match practice before we go out to Miami, hopefully timing it perfectly for the opening group game.
"I am not guaranteed to play but I am in a better position than I was two years ago. I have played a decent role in the qualifying campaign to get us to Brazil and it would be nice to get some game time and be part of a successful team.
"It is all about momentum. If we can get some decent results in the friendlies we have got before the tournament, confidence will be high."
He added: "People may be playing down our chances but momentum is a fantastic thing in football. The lads are really positive."
England meet Peru at Wembley on Friday 30 May - their final game on home soil before the World Cup. The last few tickets remain, so to make sure you don't miss out, click here to buy your tickets online.
