Vunipola broke back into the England squad last summer after an extended absence under Eddie Jones, and continued to feature across the autumn Test series.
New boss Borthwick has rung the changes for his first selection though, leaving Vunipola among a nucleus of experienced fall guys.
Saracens head coach Joe Shaw pledged the club’s total backing in helping the 30-year-old revamp his game to catch Borthwick’s eye though, especially with the autumn World Cup already looming large.
“There’s only one way you can look at it, and it will be the same when Billy has been left out before,” said Shaw. “You’ve got to listen, understand, knuckle down and get after it. There’s not a day to waste.
“The way you do that is by putting in performances for Saracens. And in many ways he’s been doing that, he’s been playing some great rugby for us. He’ll listen to Steve and what else Steve wants, and he’ll crack into that.”
Saracens’ famed tight-knit mentality will crank up another gear as Vunipola formulates his on-field response to this latest England setback. What will revolve around scrutinising and fine-tuning performance will also comprise a good dose of pastoral care.
“I think when you’ve spent 10 years of your life with somebody it’s got to be more than just a coach-player relationship,” said Shaw. “That’s why this place works so well, you care about them.
“And if people hurt or don’t get exactly what they want sometimes, you don’t shy away from it, you have to figure it out. And Billy’s long in the tooth in the terms that he’s been around a long time, and he’s not someone that will sit and wallow in self-pity.
“He’ll be straight back in the saddle, listen to Steve and the England coaches, talk to us, get a plan and then we get out there and we get better. Everybody goes through ups and downs. And Billy has been doing a lot of good stuff this year.
“We’re always trying to get better, and he’s somebody that will go through his game with the coaches all the time. And now this has happened, we’ll figure out a plan, we’ll get after it and Billy will give himself the best chance possible.”