"I'm really anxious", Benitez reiterated.
Muto, who underwent a medical and agreed personal terms with the Magpies last week, has joined on a four-year deal.
The 26-year-old has only played 25 times for Liverpool since 2015 and will be itching to get back to regular games and the chance to add to that one England cap.
"I was talking with Lee Charnley (managing director) before the game and I'll maybe see him after the game", Benitez said.
Sam Allardyce has warned Newcastle manager Rafa Benitez that he is playing a unsafe game by publicly criticising his clubs owner for his lack of backing in the transfer market.
Benitez has made five summer signings, with Japan striker Yoshinori Muto joining from Bundesliga club Mainz this week for a fee in the region of £10million.
Newcastle had already signed Mikel Merino, Martin Dubravka, Fabian Schär and Sung-yong Ki.
Muto was equally delighted after becoming the first Japanese player to represent the Magpies.
"Everyone knows that we can't compete against Man City or Man United, but we can do things in the right way".
"You're a very courageous man if you go out and criticise the owners, which to be fair is what he is doing", he told talkSPORT. We have to realise we can't make these mistakes. But when asked if there was money to spend or any deals were close he said: "I have no idea". "I don't think we'll lose any players at the moment", Benitez said. "I think we still need three or four players". "We will try our very best".
United begin their Premier League campaign August 11 with a home fixture against Tottenham.