The England midfielder was dropped for Sunday's 1-1 draw at home to Manchester United and appeared to be visibly upset when he did not feature in the match.
Barkley, once seen as the great hope around which Everton could build their side for the future, has cut a peripheral figure over the last 12 months having lost the spark which made him such a threat.
However, Koeman has no time to indulge the 23-year-old and he said must fight his way back into the team.
"He played a lot, he did not play last weekend and that is the competition we have in the squad," said the Dutchman.
"If you like to play you need to show that to the manager during the whole week and he is trying to do his best.
"We know he is one of the players who needs to bring more productivity and that is the talk we had about his situation.
"Sometimes it can be a tactical reason, sometimes I expect more from Ross Barkley but I expect more from other players offensively.
"He needs to accept it
He needs to show it on the training pitch and that is the best way to give the best answer as to why he doesn't play.
"He is always trying to do his best but it is not always about the mentality of the player, it is about tactics, his movement, his productivity and those can all be reasons he did not start last week."
Winger Yannick Bolasie looks set to have an operation on the knee ligament damage he suffered against United.
The DR Congo international, a Â£25million summer signing from Crystal Palace, has been ruled out for the season and the club are now looking at the best way forward for the 27-year-old.
"He is going to London for an opinion about his knee, what is the best thing to do and the kind of operation, and then maybe he will go somewhere else to get a second opinion," added Koeman.
"Normally I think the operation will be next week but it is a big disappointment for everyone: the player himself, his team-mates and the whole club because he is an important player."
Bolasie's absence opens the door for the likes of Kevin Mirallas and Gerard Deulofeu, bit-part players so far this season, to stake their claim but it seems likely Koeman will dip into the transfer market again in January.
"It is an opportunity for other players who maybe did not play a lot in the last few weeks and we know we need competition," he added.
"We need a big squad as it is a big month coming up with a lot of games and we need everyone at a good level.
"Still we are looking for some good options (in the transfer window) and maybe the necessity now is a little bit more than before because we have lost Yannick for a long time."
There was, at least, some good news from Seamus Coleman who returned to training on Thursday after being forced off after a clash with United striker Zlatan Ibrahimovic on Sunday.
Source : PA