Nevertheless, he has now been announced as the latest man through the door at St James' Park and will hope to establish himself as a key man for Rafa Benitez's side.
This deal was in the best interests of both clubs.
Muto completed a medical and agreed personal terms last week, but his move was only completed yesterday after receiving a work permit.
Suspected West Nile fever case in Kozhikode
Wear shoes, socks, long trousers , and a long-sleeved shirt when outdoors for long periods, or when mosquitoes are most active. State public health officials and the governor's office warned people on Thursday about increased West Nile virus activity.
Switzerland defender Fabian Schar and South Korean midfielder Ki Sung-yueng have also arrived, while Chelsea midfielder Kenedy has returned on a season-long loan deal after impressing during a six-month spell last campaign.
Benitez is a practised politician but he sounds at the end of his tether, with his latest complaints running much deeper than merely being a case of a manager putting pressure on his board before the closure of a transfer window. "I think we still need three or four players".
"Then we finished 10th and credit to our players, but I still thought we could do something more to be closer".
"When things are not going well off the pitch you can see a reflection on the pitch", Benitez told the Guardian after this week's 4-0 preseason defeat to Braga. But we can't do that at the moment. "If we don't improve everything we will suffer".
"Normally when we have time and support - we deliver".