Head coach Eddie Jones says Courtney Lawes may yet be fit to face South Africa in England's opening autumn international on November 12.
Lawes has missed Northampton Saints' recent games against Montpellier and Gloucester after suffering bruising on his knee joint.
However, Jones thinks the 27-year-old may be back to full strength in time for the Old Mutual Wealth series opener at Twickenham.
Jones is already without first-choice locks Maro Itoje and George Kruis, so the availability of Lawes would provide him with a valuable option in the second row.
"Courtney's medical situation is ongoing," Jones said.
"He probably won't train much this week, if at all. We're cautiously optimistic he'll be all right for the South Africa game."
England are currently in Portugal for a five-day training camp and captain Dylan Hartley will be put through his paces, having made just one start and one replacement appearance for Northampton since recovering from a back problem which kept him out for six weeks.
"We'll see if Dylan is ready at the end of the week," Jones said.
"We'll have a good week's training, so we'll know where every player is in terms of how ready they are to play international rugby."
A string of injuries means that England will be without 10 players for the entire autumn series, during which they will also face Fiji, Argentina and Australia.
However, Jones is optimistic about the situation, seeing it as a chance to blood some different faces.
"Rugby is a physical contact game," said Jones, who has nine wins from nine matches since taking charge after last year's World Cup disappointment.
"England pride themselves on having depth, so this is a great opportunity to show how much depth we've got.
"We've got an absolute plethora of injuries, so we're trying to work out who is going to be right and who isn't.
"But we'll get there. What I do know is that we'll have a fit 23 players who are ready to beat South Africa."