Northampton Saints' Luther Burrell has replaced Ollie Devoto in England's Six Nations squad after the Bath back suffered concussion on Saturday.
Uncapped Devoto, 22, sustained a head injury in the 24-18 Aviva Premiership defeat to Wasps and must now follow RFU protocol for concussion.
He is therefore unlikely to make his international debut in the Six Nations, with a two-week rest period required followed by gradual return to play if he is symptom fee.
Forward Josh Beaumont, 23, will also not join up with the squad after sustaining a dislocated shoulder during his game for Sale Sharks against Worcester Warriors on Saturday.
Centre Burrell has 12 caps for England but has not played since the World Cup warm-up match against France in August 2015 and missed out on the tournament squad.
He was one of 32 players assembled at Pennhyhill Park on Sunday to train for Saturday's clash with Ireland at Twickenham.
England top the table after two away wins against Scotland and Italy and prepare for successive home fixtures against Ireland and Wales.
Full squad: (Forwards) Kieran Brookes. Dan Cole, Luke Cowan-Dickie, Jack Clifford, Jamie George, Dylan Hartley, James Haskell, Paul Hill, Maro Itoje, George Kruis, Matt Kvesic, Joe Launchbury, Courtney Lawes, Joe Marler, Matt Mullan, Chris Robshaw, Billy Vunipola, Mako Vunipola.
(Backs) Mike Brown, Luther Burrell, Danny Care, Elliot Daly, Owen Farrell, George Ford, Alex Goode, Sam Hill, Jonathan Joseph, Jack Nowell, Semesa Rokoduguni, Anthony Watson, Marland Yarde, Ben Youngs.