Declan Rice, the England International's contract is set to expire in 2024, although the Hammers have an option to extend that by a further year.
So far, Rice, 24, has rejected all efforts to get him to sign an extension amid interest from virtually all of England's top clubs.
"We hope Dec stays," Moyes said.
"We would love him to be a West Ham player but we are aware that might not be the case. That is one of the scenarios.
"Our plans are to have Dec here but we are also fully aware there is a good chance that we won't have him."
England international Rice came through the youth system at West Ham and has 243 appearances in all competitions since 2017.
He has been a virtual ever-present for the Hammers this season.
Manchester City, Arsenal, Manchester United and Liverpool are among the clubs to have been linked with Rice.
"Everybody would love to have Declan Rice," former Manchester United and Bayern Munich midfielder Owen Hargreaves said on BT Sport during their coverage of Thursday's Europa Conference League semi-final first-leg win over AZ Alkmaar.
"He's playing with a little bit of swagger about him now. He sometimes kept it simple and safe but now it feels like Declan realises he can do anything on a football pitch. He doesn't have a weakness in his game.
"He would start in every Premier League team apart from Manchester City because Rodri is one of the best in the world. That is his position, he's not going to be a number 10 or eight. He can be one of the best in the world as a defensive midfielder."
Former West Ham winger Joe Cole believes Rice would walk into any team in Europe.
"He's outstanding," he said.
"Everything good that West Ham do goes through him. He's added things to his game this year. He was adding goals to his game and he can just do everything.
"He keeps getting better. Any team in Europe would have him in their team."
Former Brighton striker Glenn Murray believes Rice should be playing in the Champions League.
"At this stage of his career, Declan Rice has almost, for want of a better word, outgrown the football club," he said on BBC Radio 5 Live.
"I think he should be playing in Champions League games and for a top six club. He is a world star, and I think his star will only continue to grow and to shine."