The club are in talks with the 17-year-old over a new long-term deal, amid concerns that he could be lured away with most of the Premier League giants circling.
Everton lost Wayne Rooney to Manchester United in 2004 when he was just 18, but Moyes insists the same does not need to happen with Barkley.
"Every club will want Ross as he is going to be an outstanding player," said Moyes.
"I'm worried it will be a difficulty for us in the future.
"If someone comes for Ross I've always said it it's expensive to buy off Everton. If you're going to come and try to take our better players we don't sell cheap, that's for sure.
"I'm sure the bigger clubs will be looking at him, but we've no intention of selling. I think we've got the team to carry Ross. The club is in a much better position (than with Rooney).
"Can we carry someone like Ross now? Of course we can. Maybe when we had Wayne I didn't think we could hang on to someone of that talent, at that period."
Source: Team Talk
Source: Team Talk