Liverpool are thrilled to have Arthur on board, but the on-loan Juventus midfielder will not be available against Everton, Jurgen Klopp has confirmed.
Arthur joined Liverpool on a one-season loan on Thursday, with the Reds having an option to buy the former Barcelona playmaker for £32.3million (€37.5m).
The Brazil international did not enjoy much success across the last two seasons in Turin, and had not featured in this campaign after making just 11 Serie A starts last term.
Liverpool had initially suggested their business was complete after the early acquisitions of Darwin Nunez, Calvin Ramsay and Fabio Carvalho, but injuries to Thiago Alcantara, Naby Keita and Jordan Henderson – who will definitely miss Saturday's derby at Goodison Park – forced Klopp's hand.
Despite it being a late deal, Klopp believes Arthur is an ideal solution to Liverpool's needs.
"Everyone was really happy about the transfer. He will not have international clearance but we all hope he will be fine for Napoli [in next week's Champions League tie]," said Klopp in a press conference.
"He's a really good footballer, we all agree on that, really exciting career already and still pretty young, coming to the best age for a footballer and he can give rhythm, he's a really good passer, quick with the ball, safe on the ball, really good in tight areas, all these kind of things, I like it a lot.
"Why can you loan a player like this? Because it didn't work out 100 per cent at Juventus but I see it as a positive because the potential is still there. We play differently to Juve, and we all thought he could fit pretty well, really pleased."
Klopp indicated that Keita would remain out for a sustained period with a muscular problem, though he is hoping Thiago will return to training next week.