Ryan Crotty has had two stints out with head knocks this season, but has given himself a clean bill of health for the All Blacks this week.

Like most things Ryan Crotty does on the rugby field, the All Blacks midfielder has dealt with his twin head knocks this season with calmness, composure and a concerted plan.

And with the timing that is a hallmark of his play at either second five-eighths or centre in the test arena, the 29-year-old has himself in just the right shape to slot back in as the rock of the All Blacks midfield for Saturday night's June series opener against France at Eden Park.

With usual partner Sonny Bill Williams – aka Karaoke Bill – out with that knee injury, the All Blacks coaches would have been as relieved as anyone to see Crotty running around at Tuesday's training at full steam, and then utter some very important words afterwards.

ANDREW CORNAGA/PHOTOSPORT Ryan Crotty chats with TJ Perenara before an All Blacks training session in Auckland.

"I'm fresh and excited," declared Crotty. "I've had the last couple of weeks off but I did what needed to be done to get right, and fortunately I'm fit and available this week."

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That should see Crotty, with his 32 tests' experience, and unflappable demeanour, move in to fill Williams' No 12 jersey, alongside most likely Anton Lienert-Brown, though potentially Jack Goodhue. Goodhue has been mightily impressive in Super Rugby, but Lienert-Brown has the seniority and runs on the board in the test arena that count for so much with these coaches.

It has been a challenging season so far for Crotty with two bangs to the noggin requiring rest and patience. The last came early in the May 19 victory over the Blues at Eden Park, and has seen Crotty use the following fortnight to work through a procedure that has no room for expediency.

"You just rest till you have no symptoms," he said. "Once there are no symptoms you can start training again and gradually increase the intensity you train at.

"It's a little bit different to your hammy when it's your brain, but you're just as diligent in making sure it's right before you come back and play again.

"You know when you're right, and you know when you're not feeling right, which is probably the alarming thing. But once you do feel right again you gradually increase the training load till you're back where you were before. And that's where I am now."

Head knocks are the No 1 injury concern in rugby right now, especially given their potential to morph into something career-ending, as we have seen among several leading players in recent years.

Crotty had never got to the stage where he thought, "this could be it", but he could see how you might arrive down that dead-end road.

"You don't tend to think of it that irrationally. You go through the process. But if I wasn't to bounce back from one as quick as I tend to, then maybe you'd think that. It's never something I've thought about."

Ben Smith, set to start at fullback Saturday night, had plenty of empathy for Crotty's plight this year, having had to battle through his own spell out with head issues in 2017.

"You've just got to follow the procedure and trust the people that know. You know where you're at and how your body is feeling. The big thing is a lot of them are different -- I had a few things that led to vertigo and things like that.

"You get different symptoms, and you've got to listen to your body, be honest with the doctors, make a plan and trust that process."

Crotty showed there was nothing wrong with his top six inches when he was asked about the importance of having Smith back to provide his steel, solidity and class at the back.

"The sa-Benda-tical, as we call it," he said, referring to Smith's, er, sabbatical. "It's good to have him back ...he's a good friend to a lot of guys on the team and a great voice to have in the backs."

First up, with just a few days' preparation, you can be sure that the All Blacks will lean heavily on the cerebral, slick games of both Crotty and Smith to lead the back attack. Heady operators, both.