It is a second preparatory international for the top-ranked Irish, who spluttered past Italy with a largely second-string selection a fortnight ago and have since been on a week-long training camp in Portugal, as they fine-tune themselves for next month's tournament in France.
"I think there's a bit of nerves heading into this game," Ryan told a Friday press conference.
"It's the first game for a lot of us of this summer and playing England at home, there's always a little bit of pressure. The lads are keen to make a statement with selection and everything coming up.
"This has never been a warm-up game for us. It's been very much a Test match, that's the way we've prepared for this game all week.
"It's obviously a lot of the guys' first appearance of the summer, so it's going to be tough but we're not going to make any excuses," Ryan, deputising for the suspended Johnny Sexton, added.
Ireland, top of World Rugby's rankings, are one of the World Cup favourites after their Six Nation Grand Slam triumph. But coach Andy Farrell labelled their 33-17 victory over Italy in Dublin on August 5th "clunky".
"We must have been distracted a little bit by something. We were a little bit off. I just thought our attack wasn't where it needed to be, it wasn't as cohesive or as fluid as it usually is," Ryan explained.
"In fairness, they put us under a lot of pressure defensively. They like to get off the line quickly and be aggressive in their defence, so maybe we got a little bit spooked by that at times and we weren't as calm maybe and accurate as we needed to be off the back of it.
"There were a few lessons in the game and we need to be better tomorrow because England have a couple of games now under their belt and they will definitely be looking at this fixture as one which is as big for us as it is for them," the Irish captain added.
Ireland have a last warm-up international against Samoa in Bayonne, France on August 26th before they begin their Pool B campaign against Romania in Bordeaux on September 9th.