David Moyes has warned the West Ham players they will be dropped if they don't train or perform well enough this season.
Moyes was appointed as Slaven Bilic's successor on Tuesday after the Croatian was sacked following the 4-1 loss at home to Liverpool on Saturday.
The defeat, West Ham's sixth of the season in the Premier League, has left the Hammers sitting in the relegation zone.
And Moyes emphasised during his first press conference as West Ham boss that any player who does not show him the right attitude during training will not be picked.
He told reporters at the London Stadium: "I think if you're asking me my best attribute will be on the grass with the players, training and I hope that we can see something that's needed there.
"Once they know they are running and sprinting the least, they need to step up. If anything, it has been a little bit frantic this week - they are anxious to show, keen to show the new manager what they can do but there will be no favours.
"They will either do the work and get on with it, if they don't do the work then they are not playing. I am in a hurry and they need to be as well."
When then asked about Bilic's reported lenient style of management, Moyes responded: "I'd never criticise another manager, it is not my style.
"I can only tell you I am here and I am on a mission. If you don't run, you don't play. If you're not fit enough, you won't play. I can only tell eight of them just now but I'll tell the other eight when they get back."
The Scotsman, who has been handed a short-term contract at West Ham, also admitted he has a point to prove following disappointing spells at Sunderland, Real Sociedad and Manchester United.
He said of his appointment: "It is good for West Ham, they are getting a good manager. I do have a point to prove. Sometimes you have to repair things and I have a little bit to repair.
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"It's good for me, I'm back in and it's what I love doing. I want to do well and want the team to do well. I didn't do enough due diligence on Sunderland. Preston was very good, then everyone knows about Everton.
"I got the chance at Manchester United, which is well documented. I had a great time in Spain. I came back and made a poor choice in the club I chose."