O'Brien, who missed last Saturday's thrashing of Scotland with a skin infection that forced him to spend a week in hospital, has endured a quiet Six Nations by his own colossal standards.
It has been suggested the 25-year-old is suffering amid his move from blindside to openside flanker and that defences now know how to contain him.
But back row partner Ferris believes the reigning European player of the year remains a ferocious operator.
"Sean has shown last year in European and Test rugby that he can run through brick walls and off-load," he said.
"He was European player of the year for a reason and that doesn't change overnight.
"Maybe he hasn't got the ball enough or been in the right positions in the last couple of matches to make those breaks that he's known for, but it's definitely still in his locker.
"Hopefully if he gets his hands on the ball a bit more this weekend that you'll see a more destructive Sean O'Brien."
While O'Brien and Jamie Heaslip have been subdued throughout the Six Nations, Ferris has been at his monstrous best, especially in defence.
Long feared for his physicality and brute strength, the 26-year-old has now developed into a more rounded player with a better understanding of the game.
"I'm improving - I feel more confident on the ball these days," the Ulster forward said.
"When you're training with the lads it comes naturally. I'd like to get my hands on the ball more but it's just the way the games have panned out.
"I feel good and am really confident at the moment. I'm improving week-in, week-out. I'm feeling fit and fresh and that's the main thing."
Ferris will collide with England blindside Tom Croft at Twickenham tomorrow in a battle between two of the championship's form players.
The two became friends on the 2009 Lions tour to South Africa, with Croft taking the number six jersey that had been earmarked for Ferris until a serious knee injury forced him to return home before the Test series had begun.
"Crofty is fantastic. He's a really good athlete, somebody who I got on really well with in South Africa," he said.
"It'll be a great contest this weekend between the two of us. I've played against him a couple of times already this season in the Heineken Cup.
"I'd love to have his lineout ability. He's brilliant in the lineout and that's something I have to work hard on in training.
"Hopefully we'll cross paths a couple of times this weekend."
Ireland's bid to finish second in the championship will be led by Rory Best, who captains the side for a second successive week in the injury-enforced absence of Paul O'Connell.
Best has enjoyed a superb Six Nations and Ferris insists his Ulster skipper, who becomes Ireland's most capped hooker tomorrow with 59 appearances, has the respect of the whole squad.
"I've been fortunate to have had Rory as a captain with Ulster," he said.
"He's a guy who says what needs to be said and no more. He doesn't talk for the sake of talking. He's a great leader and has shown that on the pitch.
"Obviously he plays in the front row and there's no better place against England to put a marker down early on.
"He leads from the front and he's been tremendous over the last number of weeks."
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