Cardiff City centre-back Steven Caulker was among the players who reported for international duty with England on Monday after being drafted into the squad following three player withdrawals.
Defenders Phil Jones and Glen Johnson both dropped out of the squad after injuring themselves in Liverpool's 1-0 win over Manchester United in the Premier League on Sunday, while United striker Wayne Rooney has been ruled out with a head injury.
Caulker, 21, has one England cap to his name, having scored on his debut in a 4-2 loss to Sweden in a friendly in Stockholm last November.
Roy Hodgson's players assembled at the St George's Park national training centre in Burton, central England, ahead of the World Cup qualifiers against Moldova, at Wembley on Friday, and Ukraine, in Kiev on September 10.
England currently trail Montenegro by two points in European qualifying Group H, but have a game in hand.
Revised England squad for World Cup qualifiers against Moldova and Ukraine
Goalkeepers: Fraser Forster (Celtic/SCO), Joe Hart (Manchester City), John Ruddy (Norwich City)
Defenders: Leighton Baines (Everton), Gary Cahill (Chelsea), Steven Caulker (Cardiff City/WAL), Ashley Cole (Chelsea), Phil Jagielka (Everton), Chris Smalling (Manchester United), Kyle Walker (Tottenham Hotspur)
Midfielders: Ross Barkley (Everton), Michael Carrick (Manchester United), Tom Cleverley (Manchester United), Steven Gerrard (Liverpool), Frank Lampard (Chelsea), James Milner (Manchester City), Raheem Sterling (Liverpool), Andros Townsend (Tottenham Hotspur), Theo Walcott (Arsenal), Jack Wilshere (Arsenal)
Forwards: Jermain Defoe (Tottenham Hotspur), Rickie Lambert (Southampton), Daniel Sturridge (Liverpool), Danny Welbeck (Manchester United), Ashley Young (Manchester United)