Zach Mercer’s hand would tremble every time Eddie Jones called during his apprenticeship, but the Bath number eight is now ready to fill the vacancy available in England’s back row.

Injuries to Billy Vunipola and Nathan Hughes have ignited Mercer’s prospects of making his Test debut, presenting the 20-year-old with a shoot out against Sam Simmonds to start the NatWest 6 Nations opener against Italy on February 4.

Jones labelled him an ‘apprentice’ when he first appeared in an England training squad last year, but the hardness added to his expertise as a ball-playing forward has impressed the Australian.

Bath Rugby v Brive – European Challenge Cup – Quarter Final – Recreation Ground
Zach Mercer, left, during a European clash against Brive (David Davies/PA)

Regular conversations between the two placed Mercer on tenterhooks, but also made him aware of the elements of his game that needed improvement.

“Eddie is pretty sharp on the phone. Every time I’d get a call from him my hand would shake,” said Mercer, speaking to promote Bath’s clash with Leicester at Twickenham on April 7.

“He’s the national head coach and you don’t want to say anything you’ll regret.

“It’s literally a two-minute conversation. He says his piece and I nod my head and agree with it or we have a discussion about it then he will hang up and say ‘have a good one’.

“I seem to miss his calls first time, every time. He always leaves a voicemail and I ring back ASAP and say I am really sorry.

“The first time I spoke to him he was very genuine and told me what I needed to work on and was pretty honest with me. He got the best out of me.

“You don’t want to be on the phone longer than five minutes because you know it’s going OK when it’s shorter than that.

“Working with him is very special. His shift from being very serious to having a laugh is just like that (clicks fingers).

“You can sit at the dinner table together having a laugh and a joke and that’s why he gets the best out of players.

“Nathan is injured and Billy has been very unfortunate with injuries, but they are opportunities for me like I had at Bath with David Denton and Toby Faletau getting injured. I’m pretty good at taking the opportunities if they come.”

England Training Session – Brighton College
Eddie Jones admires the improvements Mercer has made in defence (Gareth Fuller/PA)

Mercer, son of Leeds and New Zealand rugby league great Gary Mercer, has been toiling in the gym to address the most pressing of Jones’ concerns.

“Eddie likes to see players trying stuff, but physicality was an aspect of Eddie’s work with me and I believe he’s happy how I am progressing on that front,” Mercer said.

“The main reason I didn’t tour Argentina last summer was my work rate in defence and that’s something I’ve really improved. It’s now a strong point of my game.

“I’ve been working hard in the gym to get a bit more stopping power. They’re pretty happy with my body weight, it’s more about having lean muscle.”

* ‘See Bath Rugby take on Leicester Tigers at Twickenham for The Clash, on Saturday 7th April. Tickets start from £5 for juniors, £15 for adults, available at www.bathrugby.com/theclash’