Henry Slade is expected to have surgery on Sunday after suffering a suspected broken right leg in Exeter Chiefs' Premiership victory over Wasps.
Exeter coach Rob Baxter offered a pessimistic outlook on Slade's condition following Saturday's match at the Ricoh Arena, stating: "We are pretty confident it is something pretty nasty there".
And while details of Slade's injury remained unclear the following day, his hopes of featuring for England in the Six Nations appear slim.
In a statement on the Chiefs' website, Baxter said: "Henry has an injury to the lower part of his right leg and it is envisaged he will [be] operated on sometime today [Sunday].
"At the moment we have set no timescale on how long he will be sidelined for.
"A more detailed assessment will be made following the operation."
England begin their Six Nations campaign against Scotland at Murrayfield on February 6, a match that will represent Eddie Jones' first as head coach.