Defenders Myles Kenlock and Josh Yorwerth and forwards Larsen Toure and Brett Pitman – only the former is not a summer signing – are the four in question.
Captain Luke Chambers is expected to be the only player retained from Saturday’s Championship fixture, after McCarthy, who is without the injured Jonathan Parr and Red Bishop, unusually revealed his starting XI.
Goalkeeper Dean Gerkan, Christophe Berra, Giles Coke, Jonathan Douglas, Jay Tabb and David McGoldrick are also all set to start.
Teddy Sheringham will be without Tom Hitchcock for the trip to Portman Road after he was sent off in Saturday’s 2-0 defeat against Notts County.
Hitchcock, who joined the club on a one-month loan deal from MK Dons on Friday, saw red for violent conduct in injury time.
Striker Ben Kennedy is a long-term absentee following an operation on a hip problem.
Midfielder Chris Whelpdale is also out for a lengthy period with a groin injury.