Brian O'Driscoll has beaten his stomach bug in time to equal George Gregan's world-record 139 caps in Ireland's RBS 6 Nations match against England at Twickenham on Saturday.
Stalwart centre O'Driscoll will match former Wallabies scrum-half Gregan's mammoth total this weekend as Ireland field an unchanged line-up from their impressive 26-3 Wales thumping two weeks ago.
O'Driscoll is now in line to surpass Gregan's record before retiring at the end of this Six Nations championship.
The 35-year-old will notch 131 Ireland caps in west London on Saturday, with his eight Lions honours bumping him up to equal status with Gregan.
Head coach Joe Schmidt has made two changes to the replacements bench, one enforced with lock Iain Henderson replacing Dan Tuohy who broke his arm against Wales.
Ireland boss Schmidt admitted chasing the Triple Crown at Twickenham will be the biggest challenge of his coaching career.
Schmidt said O'Driscoll could have trained on Tuesday, but that the Ireland coaches took every precaution to ensure he would be fit to face England.
"Brian trained fully on Thursday, and in fact he could have trained on Tuesday, but he just was still feeling the after effects of an illness," said Schmidt.
"And with his experience and know-how he's in a good position to know what he needs, and he brought that to bear.
"He's fully ready to go now though.
"There have been some challenges that would stand out in my mind but none as tough as this."
Captain Paul O'Connell said Ireland expect their Six Nations campaign to ratchet through the notches against England, after impressive victories over Scotland and Wales.
"The lads realise what a step up this is and there's a realistic view of where we need to be to win this match," he said.
"The confidence isn't sky-high, it's realistic.
"The last three times we've played England we've lost to them.
"The way we've been playing in recent times, particularly our last three games, we've been good.
"But in physicality, fitness and mental stakes the step up is huge.
"England have spoken a lot about making Twickenham a fortress, but we know that's exactly what it is."