But Manu, who will be leaving New Zealand within weeks to take up a contract with Edinburgh, has a plan in place to alleviate the impediment.
"If it doesn't open much more they're going to tape it up, just with a couple of butterfly strips," he said at today captain's run. "The muscle's stopped working so it doesn't want to open...but it won't stop me from playing. It's not much of an injury."
The No8 was unsure whether there would be any long-term damage but such a scenario was far from his mind on the rugby player's equivalent to Christmas Eve.
"Just one more sleep, so I can't wait," he said. "I've been here for six years and to get to the final is awesome for us. It's exciting to be able to play a final for my last game, but it's not about me. I just hope I can do well out there for the boys."
Manu has certainly played his part to date. If Aaron Smith and Lima Sopoaga are the brains of the operation, if Waisake Naholo and Patrick Osborne have provided the brawn, then Manu is unquestionably the heart of the Highlanders.
A CV that boasts international experience with only New Zealand's under-20s exemplifies the spirit of a forward pack lacking in household names but missing nothing in terms of strength and unity.
Whatever the result in Wellington, walking away from such a tight-knit team will undoubtedly be a challenge as tough as any Manu has faced on the field this season, a reality he's done his best to avoid.
"I'm trying not to think about it too much," Manu said. "I deliberately haven't packed my bags. My partner Alice told me not to pack so then my mindset is to finish here. The first job is to end on a high and do my best here."
His best has already helped the Highlanders to consecutive playoff appearances in the two years since he and Ben Smith were named co-captains. Such prosperity was a distant goal when Manu joined a lowly franchise starved of success, a rise on which he's reflected in the days leading up to his personal denouement.
"I was talking about it with Lima, about when we all came together and where we've come from, and he talked about going to the promised land. It's been an awesome six years in the making."