James Haskell looks to be a doubt for England's 2017 Six Nations opening match against France at Twickenham on 4 February.
The injury-plagued flanker, along with Harlequins' back-row Jack Clifford, did not meet up as planned with Eddie Jones' squad at their pre-tournament training camp in Vilamoura, Portugal on Monday (23 January) after making his first start of the season to help Aviva Premiership leaders Wasps book a European Champions Cup quarter-final date with Leinster thanks to a 41-27 win over Zebre in Parma.
In a statement, England said: "Both players sustained injuries in their club games on Sunday and were due to arrive in Portugal today (Monday 23 January) but will instead stay in the UK to undergo further medical assessments after which a decision will be made on when they join up with England."
Haskell played for 57 minutes against Zebre having missed the Pool 2 clash with Toulouse due to concussion suffered just 35 seconds into his comeback following six months out with a toe injury. That latter issue, which required an operation, ruled him out of the summer tour of Australia in addition to England's entire autumn international campaign.
"It's been the hardest six months of my professional career," the 31-year-old, who reported having some soreness in his foot, recently told BBC Radio 5 Live. "There was a time when I thought I was never going to make it back."
Clifford also missed dominant England's quartet of autumn victories over South Africa, Fiji, Argentina and Australia after undergoing surgery on an ankle injury. He is now said to have hurt his chest during a 27-17 defeat away to Stade Francais that saw Harlequins crash out of the Challenge Cup.
Jones, who named his 34-man Six Nations squad last week, has been beset by injuries to his pack in the build-up to England's Grand Slam title defence. Vunipola brothers Mako and Billy are both dealing with knee issues, while captain Dylan Hartley and loosehead prop Joe Marler will be further assessed this week after a six-week suspension and fractured leg respectively. Chris Robshaw has been ruled out of the whole tournament due to a shoulder injury.
Lock George Kruis was not risked by Saracens director of rugby Mark McCall during a 10-3 defeat of Toulon after recovering from a fractured cheekbone. His condition will also be assessed this week as Jones ponders the possibility of switching Maro Itoje to six.
England's five-day training stint in the Algarve ends on 27 January, when they will assemble at their usual base at Pennyhill Park in Surrey to prepare for France.