Alexander-Arnold was one of 25 players to take part in the lunchtime session, but Klopp told reporters that Liverpool had “one too many” to make the cut at the Estadio do Dragao.
Goalkeeper Marcelo Pitaluga was already due to be omitted, with the Brazilian ineligible for the Champions League, and it transpires that the decision was out of the manager’s hands.
Twenty-three players arrived in Porto, with final preparations to take place at Boavista’s training ground, but Alexander-Arnold was not part of the group.
The Liverpool Echo‘s Ian Doyle has described it as a “major scare” for Liverpool, with a cliched “race against time” ahead of Sunday’s clash with Man City, though that is highly sensationalist at this stage.
Either way, the absence of Alexander-Arnold gives Klopp a decision to make, which is certainly eased by the return of availability of Neco Williams.
Along with the young Welshman, James Milner and Joe Gomez are other options at right-back, while Klopp’s reference to “shape” as he discussed the possibility of team leaks in Portugal could even hint at a change in formation.
It seems unlikely that Klopp would field a back three, but it remains an option given the players available to him.
There were no other surprises among the group that flew to Porto, with Naby Keita joining his team-mates after a brief spell out through injury.
Liverpool squad in Porto
Defenders: Van Dijk, Matip, Gomez, Konate, Phillips, Robertson, Tsimikas, Williams
Midfielders: Henderson, Fabinho, Milner, Jones, Keita, Oxlade-Chamberlain
Forwards: Salah, Mane, Jota, Firmino, Minamino, Origi