Arthur played less than an hour from Liverpool’s Under-21 defeat by Rochdale in the Papa John’s Cup on Tuesday night.
The midfielder has made only one appearance so far for the Reds’ first-team squad following his move on loan on the appointed day from Juventus.
The Brazilian’s inactivity during pre-season means he arrived on Merseyside lacking match fitness, and it was reported last week that he has been put on a strict regimen in order to keep him awake.
Having overlooked Brazil’s squad for the September international tournament, Arthur decided not to go on vacation for the next two weeks, starting with Liverpool’s Under-21 team in the Papa John’s Cup on Tuesday.
He was replaced about an hour ago by former senior midfielder Jay Spring, who returned to the club over the summer as player and coach for the youth team.
The young Reds team retreated with a late goal from Tahvon Campbell at Crown Oil Arena, before Oludar Olofonua received two yellow cards and Liverpool ended the match with ten men.
Liverpool They have now lost both of their opening group stage matches in the Papa John’s Cup after losing 1-0 to Salford City. They next face Accrington Stanley on October 18.
Arthur could make his Premier League debut on October 1 when Brighton, who recently appointed Roberto de Zurbi to succeed Graham Potter, travel to Anfield.