England are preparing to fast-track loosehead prop Mako Vunipola into the starting XV to face Argentina in Tokyo on Saturday.
Vunipola has not started a match since Saracens' victory in the Champions Cup final against Leinster in May, because of a torn hamstring that required surgery, and has since managed only 17 minutes off the bench for England, in their World Cup warm-up match against Ireland in August, when he damaged scar tissue.
Vunipola has been edging back to full fitness, starting with a live scrummaging session during the squad's pre-tournament training camp in Miyazaki, and climaxing with an intense training session in Kobe on Friday. It has left Eddie Jones, the England head coach, with arguably the toughest selection decision of his World Cup campaign.
Joe Marler has raised his game impressively as Vunipola's deputy since the Harlequins loosehead came out of international retirement to make himself available for the World Cup campaign. Ellis Genge has proved to be explosive from the bench, typified by his 60-metre break in the victory over the United States in Kobe.
"Joe brings a real aggressive attitude to anything he does. He hits hard defensively and is a good set-piece technician," said Neal Hatley, England's scrum coach. "Against Tonga he was very good. It is not often you see Tongan forwards getting speared backwards and Joe was at the forefront of that. He scrummaged well against America. He is probably fitter than he has ever been."
