By james art The Portuguese forward picked up a rib injury in a collision during last weekend’s win over Chelsea and has not recovered in time to make it to the Emirates Stadium.
New signing Federico Chiesa has also been ruled out, but defender Connor Bradley is hoping to prove his fitness after a blow.
Slott said in a press conference on Friday: “I think they feel good, but not when it comes to playing for us at the weekend.
“Federico can train with us today or tomorrow but Diogo definitely not and Connor Bradley – let’s see if he can be with us on Sunday.”
Back-up goalkeeper Caoimhin Kelleher will continue to deputize 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 next Saturday.
Slott said of the Brazilian: “He’s progressing well, as we expect, but it’s not a short-term recovery, so it’s always difficult to judge him.
“The best way to judge an injury is in the final phase, and he’s not there yet.
“I can’t tell you how long he will be out but don’t expect him to play against Brighton in the cup or next week.”
Slot have made a superb start since taking over at Anfield in the summer, with 11 wins from their first 12 matches in all competitions and the side leading the table.
A tough 2-1 defeat at Chelsea was widely regarded as their toughest test to date, but Slott expects 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) way ahead of us but also way ahead of Chelsea.
“So you would imagine playing Arsenal would be more difficult.
“Let’s see at the end of the season where both Chelsea and Arsenal are, but normally you expect, especially as it’s an away game, that this one is more difficult than Chelsea at home – and we all saw how difficult Chelsea were at home. “
Slot has no doubt that Liverpool’s title run will be measured in their games against Arsenal and champions Manchester City, who face them on December 1.
He said: “No one knows at this stage who your competition will be, but I think we all know Arsenal will be one of them.
“Getting points dropped or getting points against them is always important. I think last season it was three draws and one loss (against the top two) so if you use the maths if Liverpool could have won them all the league table would have been a bit different.
“It’s hard to win away from home against Arsenal or City, but that’s something we’re trying to do on Sunday, for sure.”