Deacon's availability is a huge boost for the English Champions, with the 29-year-old set to make his 199th start if selected in Dublin.
"I'm feeling good. These have been my first sessions back for a few weeks now and I've declared myself fit," said Deacon.
"It's the biggest game of the season so you've got to be right, but I'm confident that I'm 100 per cent."
If Deacon does get thrown straight back into the mix for the Heineken Cup quarter final it will be his first outing since the defeat to Ireland at the same stadium three weeks ago but a lack of game time doesn't worry the softly-spoken second row.
"I was thinking about that myself when I was away with England," added Deacon.
"You'd have these fallow weeks where you'd play a massive match and then you don't have a game the following week, and then you play again.
"I've played big games for England and I want to play in big games for Leicester. That's how I'm looking at it."
Club games don't come much bigger than this and Deacon is fully aware of the size of the task that lies ahead.
Facing a Leinster side who stormed through one of the toughest pools in Heineken Cup history in their home city in front of a crowd of more than 50,000 is undoubtedly a big task.
But never one to shy away from a challenge, Tigers fans will know that Deacon is exactly the type of player you want on your side when appearing on the big stage.
Leicester born and bred, Deacon's role has so often been undervalued outside the East Midlands but the Welford Road faithful have rarely doubted his impact on the country's most successful professional side.
Deacon might not make the eye catching breaks or the flashy offloads that bring public or media attention but what he does do is the hard graft, the uncompromising, thankless tasks that set the platform for those around him to succeed.
And against a side of the quality of Leinster, those attributes could play a major part in determining whether Leicester are celebrating or commiserating in Dublin's fair city on Saturday night.
"Most games are probably won up front. Set piece will be key to the game, both scrum and lineout. It will definitely be a huge challenge.
"What Leinster are pretty good at is slowing the opposition ball down, just like Ireland and Munster are so maybe it's an Irish thing. They're good over the ball and good in the tackle area and that's a key area this weekend.
"Sean O'Brien's in there, Cian Healy and Mike Ross has done really well for them and for Ireland as well. Then there's Leo (Cullen) in there in the second row as well so they've good got players all across the board.
"Leo's one of those guys who just gets on with the game. You could say we're similar players. We actually worked quite well together when he was here at Leicester. He was very calm, always got on with his job and was one of those trustworthy guys that you knew would perform on the day."
Deacon knows that a good start in the Irish capital will be crucial to his side's chances of progression to the semi-final stages, especially as he was part of an England side that saw their Grand Slam dream ripped apart in the opening 30 minutes of their own decisive Dublin encounter.
Leicester will arrive at the Aviva in good spirits having recorded six successive Premiership and European away wins since defeat to Perpignan in mid December.
And while there is no public suggestion of revenge for their Heineken Cup Final defeat to Saturday's opposition two seasons ago, victory this time around would be a momentous occasion for Deacon and his fellow Tigers.
"The guys are really confident as they've done well through the international period. The mood's good. It's a big challenge but we're going well at the minute.
"We had a big win against Bath and we then beat Quins away from home. That probably wasn't the performance we wanted but we ground out the win, which is always important.
"That Heineken Cup Final loss was a few years back and it does seem a while ago. We've moved on and so have they but it's a massive game. We want to do well in this competition and go further than the quarter final because we didn't make the knockout stages last year.
"But we need to start well. We need to control the ball, look after it and not give it away. If you go back to that England game, we didn't have the ball for 30 minutes and, when we did, we gave it straight back. That puts pressure on you.
"We've got to look after those areas of the game, control the set piece and get into the game early."