Vunipola refractured his right arm during England’s tour of South Africa, just two months after returning to action following an initial break suffered in January.
The 25-year-old Sarries number eight has avoided surgery and resumed work with the Gallagher Premiership champions.
“His arm’s fine, his arm’s healing well, he’s back in the club. He’s been doing bits and bobs and he’ll be back in the week after next, not full training but rehab,” said Sanderson, speaking at the Premiership fixture launch.
“I think whenever he plays for any length of time, Billy’s going to have a big season.
“I hope and I pray and I think the bad luck he’s had might have come at the right time for him with respect to England and this World Cup; that he’ll see this World Cup through injury-free because he’s a big part to play in that side as well.
“Every time Bill’s come back, he’s been better for it.”
Woke up this morning as a genuine book winner! Last night my book Wrecking Ball won Rugby Book of the Year at the Sport Book Awards 2018 @sportbookawards #SBA18 Thanks @Wasserman & @GershonPortnoi 🙌🙌 #WreckingBall pic.twitter.com/RSwVd53GdS— Billy Vunipola (@bvunipola) June 8, 2018
Vunipola has been plagued with injuries, dating back to the 2015 World Cup when he was ruled out of the tournament with knee ligament damage sustained during the pool stages.
He suffered a further knee problem the following year before missing the British and Irish Lions’ tour of New Zealand last autumn while undergoing surgery.
His initial arm break came at the start of the year when playing for Saracens against Ospreys, ruling him out for four months, and he then was forced off in the first half of his country’s second Test against the Springboks in Bloemfontein on June 17.
Saracens begin the new Premiership season at Newcastle on September 2, with the World Cup in Japan scheduled to start 12 months later.
And Sanderson, who was forced to retire at the age of 26 due to injury, believes the mental challenge of being sidelined is the biggest hurdle facing Vunipola.
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“It’s more so his head, it’s his third time he’s been through it,” added Sanderson.
“I think it’s the toughest thing because as soon as you get injured, you’re out of the squad. You feel out of the squad, even if you’re not.
“Every player goes through injuries and it’s how you come out the other side that will determine the kind of player you’re going to be. I didn’t come out the other side; Billy will.
“You either let the injury affect you mentally and physically and then try and get back to near where you were, or you use the time when you’re injured to get bigger and stronger and faster to become a better player, cognitively-speaking.”
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