The Dutchman completed his £24m move from Arsenal to Old Trafford last week but will have to wait until the last minute before knowing if he will make his club debut against the Toffees on Monday night.
Despite praising United's capture of Van Persie, Moyes is adamant that Everton will do all they can to prevent the 29-year-old from having a dream debut.
"I think United have made some good signings, bought some young players and bought one who is maybe a little bit older than they normally do," Moyes said.
"But he's a seriously good player who you would expect will make a big difference. He will be a big help to an already good side.
"But we will be ready for Manchester United. We want to get the season off on the right note."
Everton have lost their last four opening games of the Premier League season.