Liverpool manager Jurgen Klopp has conceded that new signing Arthur will not be available for Saturday's Merseyside derby with Everton in the Premier League.
The Brazil international arrived on a season-long loan from Juventus on transfer deadline day following injuries to Jordan Henderson, Naby Keita, Thiago Alcantara and Alex Oxlade-Chamberlain.
Liverpool's midfield options have been left severely depleted by injuries in recent weeks, and Arthur was thought to be in with a chance of making his debut against Everton.
However, speaking at his pre-game press conference, Klopp admitted that Arthur's international clearance was unlikely to come through before next week's Champions League opener with Napoli.
"I'm really happy about this transfer. My info is international clearance will not happen until tomorrow. We all hope he will be fine for Napoli," Klopp told reporters.
"He is a really good footballer, who has had a very exciting career already and is still pretty young. He is coming into best age for a footballer [26 years of age].
"He gives us rhythm, he is a really good passer, has speed with the ball, and is safe on the ball. He is really good in tight areas so I like the transfer a lot. Why can you loan a player like this?
"Didn't work out 100% at Juventus. I see it as positive because potential is still there. We play differently to Juventus. I thought could fit pretty well so we're really pleased."
Liverpool have been working around numerous absentees during the embryonic stages of the new season, and Klopp gave a lengthy fitness update on the likes of Henderson, Thiago, Keita, Diogo Jota and Ibrahima Konate.
Klopp had good news to share on Jota, who could be back with the squad following a lengthy period out with a hamstring problem, while Thiago is not too far away from a return to training either.
However, captain Henderson will definitely miss the Merseyside derby with the injury he picked up against Newcastle, but Klopp is unsure of the extent of the England international's problem.
"We are still waiting for the result on Hendo [Jordan Henderson, hamstring]. We've heard nothing yet. He's definitely out, just don't know the extent. [Naby] Keita is a muscle injury. Ox [Alex Oxlade-Chamberlain] is a muscle injury and he will be out for a while," Klopp added.
"Calvin Ramsay is still out, getting closer and closer, it's his back. Something to do with age and growing. He hasn't trained with us properly.
"Thiago is the closest of them all. At the start of next week he will be in team training. Ibou [Ibrahima Konate] is not too far away. In and around the international break he will be back in training.
"Diogo probably will be in as well, he trained yesterday with the team first time. He will train today. I have to make a decision, does it make sense that we involve him already or not? But if, it is the first time we have five attackers – sounds like Christmas!"
Jota's fellow attacker Darwin Nunez also returns from a three-match suspension for the trip to Goodison Park, where Liverpool will aim to improve on their sixth-placed standing in the Premier League table. body check tags ::
