The England international has decided against signing a new contract at Goodison Park and is widely expected to be sold by the Toffees this summer, as they risk losing him as a free agent in 12 months' time.
Koeman is unsure exactly what the future holds for the 23-year-old, although he did confirm that he expects "one or two more" players to be signed before the transfer window closes.
"At the moment, it's not a clear situation," he told reporters. "[Barkley is] not fit, that's why he didn't travel. We'll see what happens."
Barkley has been at Everton for the past 12 years, racking up 179 senior appearances for the club and scoring 27 goals during that time.