Frank Lampard has urged Christian Pulisic to show he deserves to play more for Chelsea after his slow start to life in England.
The American winger was left out of the Blues' squad for their midweek Champions League win in Lille, and has not played in the Premier League since August.
Pulisic, who joined Chelsea for £57.6m this summer after signing the deal in January, will hope to return for their game at Southampton on Sunday, live on Sky Sports, but Lampard said: "I spoke to him and was very clear about the standards.
"We have to give him the fact he's moved country and moved leagues. He's just turned 21 so I think, if anyone is getting too excited about this, they should calm down.
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"What he needs to do is work to show within the group that he deserves to play. That's what the focus on everyone is."
Callum Hudson-Odoi's return from injury has pushed Pulisic further down the pecking order, although Lampard said "he needs to learn" despite scoring on his return against Grimsby last month.
The England international responded with assists off the bench against Brighton and Lille, and the head coach praised his reaction.
"I'm really pleased and that has to continue," Lampard said of Hudson-Odoi's form. "We can all focus on Pulisic but Callum's the same.
"Sometimes as a manager you want more. You have to be honest and the players have to react.
"Callum has two assists in the games [when] he's come on and that's what you want; to keep pushing."
Ruben Loftus-Cheek is expected to follow Hudson-Odoi by returning from a lengthy injury in the next few months, increasing Lampard's options further.
Ross Barkley was also left out of the Chelsea squad in Lille, and Lampard warned he will have more tough decisions to make in future.
"This is one of my difficult problems in this job," he conceded. "I have good players and everyone has a story.
"Pulisic has a price tag, Barkley is an international player, Mason Mount is an international player, Callum Hudson-Odoi just signed a new contract, Bayern Munich wanted to buy him last summer and he's an international player.
"Ruben Loftus-Cheek will come back and be an international player. I can't pick them all.
"All I have to demand of them is that they show me in training and show me they are worthy of the place.
"It's just my job. Next week you might be asking me about two other names. It's the competition that we have."