The ex-Everton icon was part of the Three Lions' senior set-up from 2008-2016, where he made 40 caps and was called up to two major tournaments.
During his time playing for England, he rubbed shoulders with Steven Gerrard, Wayne Rooney, Harry Kane, David Beckham and Rio Ferdinand among others.
But the 41-year-old has stated that while Gerrard was excellent, it was Chelsea legends Terry and Lampard, along with Ferdinand, that left him stunned.
Speaking on talkSPORT Drive, Jagielka commented on the step-up from training with his Everton teammates to playing with England's stars on international duty.
He said: "These are the people I was used to watching, especially when I was first getting in the squads, your Rios, your JTs [John Terry].
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"[They won the] Champions League, [Premier League] championships and all sorts, so I think when I got there, you're always quite confident, but a little bit apprehensive for the first couple of times.
"But to see the standard, I watched a shooting drill, I don't think anyone missed, and I'm thinking to myself, 'This is not what I'm used to.'
"People would always question, 'Oh who is better, Lampard, Gerrard, [Paul] Scholes...', and you'd have your own opinion.
"But I don't think Frank missed one shot, some of them don't even look clean and they'd go in the bottom corner.
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"It was like, 'It can't be lucky' - it was an ability, it was the next level.
"Even like JT, he would join in on possession [drills], normally the centre-halves would stand on the outside.
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"And midfielders and creative players would be in the middle where it's technically harder with more bodies around you.
"And he was stepping in, left foot, right foot, Rio [Ferdinand] doing the same.
"You're thinking, 'Maybe I'm going to have to do this', but I wouldn't ruin a few sessions yet, I'd wait a bit later before I started ruining!
"But it did give you an idea of where you were at, we're talking about amazing teams with amazing centre-halves.
"And it was tough, it was an experience, but international duty, it's always better when you play and I was desperate to try and get in the squad and then get some games."