Manchester United boss Jose Mourinho has emphasised his players have to earn the right to be selected after leaving Anthony Martial out of his latest matchday squad.
Although available, forward Martial, having started the previous game, was not part of the United 18 for Thursday's 4-0 Europa League win over Feyenoord.
Martial scored 17 goals in his first season with United last term, but has netted only twice so far in 2016-17.
When asked about the 20-year-old Frenchman's omission, Mourinho confirmed Martial had not been injured, spoke of how he had wanted to bring Henrikh Mkhitaryan into the team and then added that "players...have to win their positions".
Mourinho said of Martial: "He was okay for the game, it was just an option.
"He played on Saturday (in the 1-1 draw against Arsenal) and I cannot play with 12 players. I cannot have, (with those) on the bench, 19 or 20.
"You wanted to see Mkhitaryan (who shone on what was only his second United start) and I wanted to too. I cannot play all of them at the same time.
"Anthony played against Arsenal, and (Thursday) was the moment to give a chance to Mkhitaryan to start.
"So it was just an option - and I think the players, they have to win their positions.
"They are friends, they are colleagues, they work together every day, but in the end they compete between themselves to have more chances to play."
Last season Martial was working under the management of Louis van Gaal, whose style of play drew plenty of criticism.
Mourinho says Martial may have been more "comfortable" with that brand of football and has suggested he therefore needs time.
But the Portuguese has also stressed he has several forward options to choose from and that it is important for players to make the most of their opportunities.
Asked if he felt Martial was suffering from 'second season syndrome', Mourinho said: "First of all, the teams are very different.
"The way the team played last season - and I'm not saying better or worse, just different - was probably more adapted to Anthony.
"Probably he was feeling more comfortable playing that way, at that intensity, at that rhythm of the ball possession and ball circulation. So probably he needs also some time.
"But in our squad, for these positions, we have Mkhitaryan, (Jesse) Lingard, (Memphis) Depay, (Juan) Mata, (Marcus) Rashford, Martial. These are probably the positions where we have more options.
"And, you have one opportunity, you have two, you have three - if you don't bite then somebody comes and takes the meat."
Ahead of Sunday's Premier League home clash with West Ham, United are sixth in the table, nine points behind leaders Chelsea.
Mounting a genuine title challenge is looking a tough ask for the Red Devils, but Mourinho, referring to the 2014-15 campaign in which he guided Chelsea to the trophy, said: "When I won the last title 18 years ago - sorry, 18 months ago - I had something like 10 points advantage and then in one month I had the same points as Man City.
"We recovered and won that title. But you can recover points. Other teams can lose points. During the season there are moments where everything goes against you and where everything goes in your favour.
"We know that the game is not over - but the reality is that there is a distance, and there are many quality teams.
"It's a very difficult competition, but let's go match by match and see what happens. We play another difficult game on Sunday - let's see if we can get the three points."