By SABC Sport
25th October 2024
The Portuguese forward suffered a rib injury in a collision during last weekend's victory over Chelsea and has not recovered in time to make the journey to the Emirates Stadium.
New signing Federico Chiesa is also ruled out but defender Conor Bradley is hoping to prove his fitness after a knock.
Slot said at a press conference on Friday: "I think they feel good but not when it comes to playing for us at the weekend.
"Federico might train with us today or tomorrow but Diogo definitely not and Conor Bradley, let's see if he can be with us on Sunday."
Back-up goalkeeper Caoimhin Kelleher will continue to deputise for Alisson Becker, whose return date from a thigh injury remains unclear.
Liverpool travel to Brighton in the Carabao Cup next Wednesday before hosting the Seagulls in the Premier League the following Saturday.
Slot said of the Brazilian: "He is progressing well, like we expect, but it is not a short-term recovery so it is always difficult to judge him.
"The best way to judge an injury is in the end phase and he is not there yet.
"I can't tell you how long he will be out but don't expect him to be in against Brighton in the cup or next week."
Slot has made a superb start since taking over at Anfield in the summer, with 11 wins from his first 12 games in all competitions and his side top of the table.
The hard-fought 2-1 defeat of Chelsea was generally considered to be their toughest test to date but Slot is expecting another step up against the Gunners, runners-up for the past two seasons.
The Dutchman said: "I expect a lot from Chelsea this season and they showed it at Anfield.
"But if you look at the last two seasons, Arsenal were (not only) far ahead of us, but also above Chelsea.
"So you would assume that playing Arsenal will be more difficult.
"Let's see at the end of the season where Chelsea and Arsenal both are but normally you expect, especially as it is an away game, that this one is more difficult than Chelsea at home â- and we all saw how difficult Chelsea at home was."
Slot has no doubt Liverpool's title credentials will be measured in their games against the likes of Arsenal and champions Manchester City, who they face on December 1.
He said: "Nobody knows at this stage who is going to be your competitor, but I think we all know Arsenal will be one of them.
"Dropping points or winning points against them is always important. I think it was three draws and one loss last season (against the top two), so if you use mathematics, if Liverpool could have won all of them the league table would have been a bit different.
"It is difficult to win in an away leg against Arsenal or City but it is something we are trying on Sunday, definitely."