From 2018-19 registered squad list
Bailly, Eric Bertrand
Darmian, Matteo
De Gea Quintana, David
Grant, Lee Anderson*
Hoelgebaum Pereira, Andreas Hugo*
Jones, Philip Anthony*
Lindelof, Victor Jorgen Nilsson
Lingard, Jesse Ellis*
Lukaku, Romelu Menama*
Martial, Anthony Joran
Mata Garcia, Juan Manuel
Matic, Nemanja
McTominay, Scott*
Pogba, Paul Labile*
Rojo, Faustino Marcos Alberto
Romero, Sergio German
Sanchez, Alexis
Santos, Frederico Rodrigues De Paula
Shaw, Luke Paul Hoare*
Smalling, Christopher*
Young, Ashley Simon*
This is excluding Fellaini, Herrera and Valencia.
That's 21 players. This year we have added AWB, Daniel James, Tuanzebe and Rashford. That's 25.
Also this is excluding Joel Pereira who wasn't included last season. So if we sign anyone, we have to leave few players from the registration squad (If we fail to offload them).