Southgate has today named an initial 33-man squad, before cutting that down to 26 by June 1.
This is partly to give time for those battling injury to prove their fitness, with Henderson among those after he spent the last three months out with a groin problem.
There is a place for Alexander-Arnold at this stage, though strangely Southgate is believed to prefer other options at right-back.
Chelsea’s Reece James is among those named in the provisional squad, along with Kieran Trippier and Kyle Walker.
Question marks over Alexander-Arnold’s place at the tournament are baffling, with the 22-year-old one of the best right-backs in world football.
Goalkeepers: Jordan Pickford, Dean Henderson, Sam Johnstone, Aaron Ramsdale
Defenders: Harry Maguire, John Stones, Conor Coady, Tyrone Mings, Ben Godfrey, Ben White, Trent Alexander-Arnold, Ben Chilwell, Luke Shaw, Kieran Trippier, Kyle Walker, Reece James
Midfielders: Jordan Henderson, Declan Rice, Mason Mount, Kalvin Phillips, Jesse Lingard, Jude Bellingham, James Ward-Prowse
Forwards: Harry Kane, Marcus Rashford, Jack Grealish, Dominic Calvert-Lewin, Jadon Sancho, Raheem Sterling, Phil Foden, Mason Greenwood, Ollie Watkins, Bukayo Saka