Brad Shields missed training on Tuesday morning to put his involvement in England's Guinness Six Nations clash with Ireland in doubt.
Shields has been struggling with a side strain and was already a doubt for Saturday's opener at the Aviva Stadium before sitting out the session at the squad's Algarve training camp.
If the Kiwi-born Wasps back row is ruled out, Mark Wilson is likely to fill in at blindside flanker.
Wilson was named England's player of the series last autumn with three superb appearances at number eight and one at openside flanker propelling him into World Cup contention.
The 29-year-old, who recently recovered from a shoulder injury, plays most of his club rugby at Newcastle in the number six jersey.
Ben Te'o was also absent from training, although the Worcester centre is not known to be injured.
Eddie Jones reduces his 35-man squad later today when a number of players will return home, before naming his team for the Dublin clash on Thursday.