The Everton defender believes the fight for a place in next summer's World Cup squad will not truly begin in earnest until closer to the end of the current Premier League campaign
Terry, 32, has been backed to return to the Three Lions set-up by both Blues manager Jose Mourinho and former coach Ray Wilkins.
Everton skipper Jagielka has established a centre-back partnership with Terry's club team-mate Gary Cahill as England finished top of their World Cup qualification group but feels the former skipper could feature in Brazil.
"If John Terry feels that's what he wants to do, he's playing well for Chelsea at the moment so anything's possible," he told reporters.
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Roy Hodgson will have another chance to assess the players at his disposal during friendlies against Chile and Germany, but Jagielka says the fight for a place on the plane to Brazil will not truly begin until closer to the end of the domestic campaign.
He continued: "The manager will know who he wants and who he doesn't want. A lot can happen even after next week's games so if you get a chance to play, you want to play well and put down a marker but I don't think the scrap quite starts yet. That'll be more towards the end of the season.
"It's nice to be able to go there and have two friendly games, especially as there was the potential for them not to be friendlies at one point.
"We have two fantastic teams to play against, both at home, and hopefully we'll get a decent turnout in both games. It's all good stuff before the finals in Brazil."
Jagielka insists he is relishing the prospect of a testing month ahead, with the visit of high-flying Luis Suarez and Liverpool awaiting Everton after the international break.
He said: "It would be daft of me to be thinking about [the derby] before I've played the two games for England.
"If you start looking too far in advance you're only going to trip yourself up in the games you play in the meantime.
"It's not just Luis Suarez, Liverpool are in fantastic form - his strike partner [Daniel Sturridge] is not doing too badly either.
"I'll go out there, whether I'm playing against my little boy in the back garden or international players, for club or country, trying to do my best.
"The derby itself writes headlines and if he [Suarez] scores goals, as he has done, he's going to be part of that. That's down to us to make sure it's not him writing the headlines and us this time."