London - England star Billy Vunipola is set to miss the Six Nations after breaking an arm for the fourth time in two years, Premiership club Saracens announced on Monday.
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His injury heaped more misery on the English champions, who on Saturday had been told they would be relegated at the end of the season for salary cap breaches.
The 27-year-old No 8 suffered the injury early in Saracens' 27-24 victory over French side Racing 92 on Sunday, which kept their hopes alive of a successful European Champions Cup title defence.
"Billy Vunipola has suffered a broken arm," read a club statement. "He will see a consultant over the coming days to determine the full extent of the injury before undergoing rehabilitation."
The 51-times capped Australia-born forward has broken his right arm twice and his left once.
Saracens' statement was released just hours before England coach Eddie Jones announced a 34-man squad for the upcoming Six Nations Championship, although he opted against calling up specialist cover for Vunipola.
Powerful wing Jack Nowell and veteran prop Dan Cole were the most high-profile of the 10 absentees from the squad that took England all the way to November's World Cup final in Japan, where Jones's men were well beaten 32-12 by South Africa.
Wasps flyhalf Jacob Umaga, the nephew of former New Zealand captain Tana, was among eight uncapped players in a squad that will travel to Portugal on Thursday for a pre-tournament training camp.
England, runners-up in last season's Six Nations, begin their 2020 title quest away to France in Paris on February 2.
"It is always about winning the next game so we have picked the best squad available," Jones said in a Rugby Football Union statement.
"At the same time we wanted to bring some young players in because we need to keep building our depth so for those new players it's an exciting opportunity for them."
Earlier, England announced that Steve Borthwick, Jones's long-serving assistant, would leave his post at the end of the season, with Jason Ryles replacing him in November.
Former England captain Borthwick was also alongside Jones when the latter was in charge of Japan.
"I have had a great seven years with Steve," said Jones. "He is a loyal, hard-working and analytical coach but I understand he needs now to get out on his own following this campaign."
England 34-man squad for the 2020 Six Nations announced on Monday:
Elliot Daly (Saracens), Ollie Devoto (Exeter), Fraser Dingwall (Northampton), Owen Farrell (Saracens), George Ford (Leicester), George Furbank (Northampton), Willi Heinz (Gloucester), Jonathan Joseph (Bath), Jonny May (Leicester), Ollie Thorley (Gloucester), Manu Tuilagi (Leicester), Jacob Umaga (Wasps), Anthony Watson (Bath), Ben Youngs (Leicester)
Luke Cowan-Dickie (Exeter), Tom Curry (Sale), Tom Dunn (Bath), Ben Earl (Saracens), Charlie Ewels (Bath), Ellis Genge (Leicester), Jamie George (Saracens), Ted Hill (Worcester), Maro Itoje (Saracens), George Kruis (Saracens), Joe Launchbury (Wasps), Courtney Lawes (Northampton), Lewis Ludlam (Northampton), Joe Marler (Harlequins), Alex Moon (Northampton), Kyle Sinckler (Harlequins), Will Stuart (Bath), Sam Underhill (Bath), Mako Vunipola (Saracens), Harry Williams (Exeter)
Fixtures (SA times):
February 2: France v England, Paris - 17:00
February 8: Scotland v England, Murrayfield - 18:45
February 23: England v Ireland, Twickenham - 17:00
March 7: England v Wales, Twickenham - 18:45
March 14: Italy v England, Rome - 18:45