The Reds initially registered 23 players for their clashes with LASK, Union SG and Toulouse, but this could be added to prior to any matchday.
UEFA rules stipulate that, beyond a senior squad of up to 25 players, an unlimited number of under-21s are eligible if they have been with the club for upwards of two years.
Ahead of their trip to LASK to kick off the Europa League, Liverpool have named a further 12 in their squad as part of List B.
Also registered is Conor Bradley, who stands to figure prominently this season but is currently sidelined with a stress fracture in his back.
The majority of those named were part of Jurgen Klopp‘s squad for pre-season, with goalkeepers Marcelo Pitaluga and Fabian Mrozek, full-back Calum Scanlon, midfielders James McConnell and Melkamu Frauendorf and striker Lewis Koumas in.
Luke Chambers is also available having seen proposed loan moves to Bayer Leverkusen and Swansea fall through.
And completing the group is Gordon, who made his long-awaited return from injury as Liverpool U21s lost 4-1 to Middlesbrough at the start of the month.
Gordon had been out for 19 months with a series of growth-related injuries, but is now working his way back to full fitness at youth level.
He should not be expected to be heavily involved in the Europa League, as with many of the others now registered, but his inclusion is a show of faith from the senior staff.
Liverpool’s Europa League squad
Goalkeepers: Alisson, Kelleher, Pitaluga*, Jaros, Mrozek*
Defenders: Van Dijk, Konate, Gomez, Matip, Quansah*, Chambers*, Alexander-Arnold, Robertson, Tsimikas, Bradley*, Scanlon*
Midfielders: Szoboszlai, Mac Allister, Thiago, Gravenberch, Jones, Elliott*, Endo, Bajcetic*, Clark, Frauendorf*, McConnell*
Forwards: Salah, Diaz, Gakpo, Nunez, Jota, Doak, Gordon*, Koumas*
* List B