The Toffees confirmed on Monday evening (17 July) that the playmaker, who also did not travel to Tanzania last week for a match against Kenyan club Gor Mahia, did not feature in a 25-man group that flew to the Netherlands ahead of a friendly clash with FC Twente later this week and will subsequently move onto Belgium for a meeting with Genk.
While Everton insist his absence is due to a lingering groin injury, Barkley's continued non-appearances will do little to dampen speculation that he is set to leave Goodison Park over the coming weeks.
The 23-year-old has now entered the final 12 months of his contract and is said to have rejected fresh terms of approximately £100,000-per-week ($130,000).
Manager Ronald Koeman, who wants to sign Gylfi Sigurdsson from Swansea City, previously stated that the player would need to agree an extension before the end of the 2016-17 season or else be sold.
Tottenham have long been mentioned in connection with Barkley, although until now appear to have been put off by his hefty £50m valuation. However, The Independent reports that Spurs are preparing to step up their pursuit of the 22-cap England midfielder, with Everton ready to compromise on their asking price as they look to avoid losing him for nothing next summer.
Ramiro Funes Mori has also been left behind as the Argentine centre-back continues to recover from a torn meniscus suffered on international duty back in March. However, former Southampton right-back Cuco Martina was on the plane after completing a free transfer to Merseyside that sees him reunite with his old Saints boss Koeman.
"Cuco Martina is an experienced player who can perform in different positions at the back, which is important," the manager said of a player with whom he is very familiar. "It's also important, with the number of games we will face in the coming campaign, that we have strength and competition in the squad.
"I brought the player to Southampton, so I know what he can do for us here and this is why I've now brought him to Everton. He is a player who will strengthen our squad and be able to play in different positions when that's needed, too."
Along with Martina, fellow new signings Jordan Pickford and Sandro Ramirez also travelled to the eastern Dutch city of Enschede having been given time off following their respective exploits at the recent European Under-21 Championship in Poland.