However, we may have issues agreeing on a transfer fee for our top two left-back targets so a move for the West Brom fullback can not be ruled out.
Announcing the news on their official website, Newcastle's statement claimed Rondon was Benitez's "number one transfer target" this summer.
"I'm honoured to be a player for such a big club", said Muto, the first Japanese player to join Newcastle.
Newcastle had already signed Mikel Merino, Martin Dubravka, Fabian Schär and Sung-yong Ki.
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.
Newcastle have completed the signing of West Brom striker Salomon Rondon on a season-long loan deal, with Dwight Gayle moving in the other direction as part of the agreement.
"We are concerned. Everyone in the dressing room was really upset with our performance and with how things are going, but we will try to change things in the next 10 days".
Gayle, meanwhile, netted six Premier League goals for Newcastle last season, a year after scoring 23 times for the club in the Championship.
Formerly of Malaga, Las Palmas and Zenit St Petersburg, Rondon is on the move after three years with West Brom, as he was always unlikely to stay and play in the Championship following their relegation.