Walker had been in doubt for the historic season opener at Allegiant Stadium, after being ruled out of last month's All Stars clash due to a calf strain.
There had been fears the five-eighth would add to South Sydney's unavailable list, with Jack Wighton and Campbell Graham already missing the clash.
But one of the game's most lively players managed to come through training unscathed this week and is now certain to face the Sea Eagles on Saturday night (Sunday AEDT).
"He's a world-class player. Really happy that he was able to get the training done in San Diego," coach Jason Demetriou said.
"That was important for his prep, to be able to have a full week of training going into round one.
"It's got him in a good headspace and the team will benefit from that for sure."
Manly have also confirmed Luke Brooks will play, after he spent time away from teammates at training this week while battling a minor injury.
Brooks's first game for Manly has largely been overshadowed by the Vegas extraordinaire, with the 29-year-old happy not to be the centre of attention.
The No.6 has worn the weight of the world on his shoulders for much of his career at struggling Wests Tigers.
Even on the night of his 200th game last year, Brooks cut a tense figure after a 66-18 win over North Queensland while discussing if he wanted to leave the Tigers.
Fast-forward nine months and Brooks appears a completely different person.
No longer needing to be the reason behind every win or loss, Brooks has seemed more relaxed in the weeks leading up to Vegas.
"We think a change might be good for him," coach Anthony Seibold said.
"He doesn't have to be the playmaker in our team. We've got Tom (Trbojevic) and Daly Cherry-Evans who are our organisers.
"We just want him to bring his running game. He's got a great left-foot kick. He's a brave guy too, gets his body in front in defence.
"He's got to come in and try and adapt to our play. It's not going to be perfect to start with, there's going to be some issues in and around cohesion for our spine.
"But we feel like we'll get better the more they play together."
Seibold suggested Manly's attacking players may need to play tighter on the skinnier Allegiant Stadium field, with three metres shaved off each side.
Field position is likely to become more important with the field also six metres shorter.
"The middle third is going to be so important because defence is probably going to be more compressed," Seibold said.
"For us it's about trying to disrupt what guys like Cam Murray and Damien Cook, Latrell (Mitchell) and Cody can do.
"We want to try and use our weapons where we can, but it is different."
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