The Egypt international was an unused substitute for Sunday's win at West Ham and was on the bench for the 1-1 draw at home to Sunderland on Wednesday.
It was the first time in his Anfield career that he had not started in back-to-back league matches.
The forward was brought on for the second half against Sunderland but struggled to make an impact and is now goalless in five matches.
Salah has scored just four Premier League goals for the struggling defending champions this season, in stark contrast to his haul of 29 last season.
Liverpool captain Van Dijk was asked after the Sunderland draw whether Salah's omission had sent a message to the dressing room.
"That's always been the case," he said. "It's not like you have unlimited credit, everyone has to perform.
"Mo has been doing that but the manager made that decision in the last two games. We all want the best for the club.
"I am pretty sure Mo will still be a big part of what we are trying to achieve because he is an amazing player and he has shown it consistently."
Van Dijk praised playmaker Florian Wirtz, whose shot deflected in off Sunderland defender Nordi Mukiele for a late Liverpool equaliser that left them eighth in the table.
The German, who joined Liverpool from Bayer Leverkusen in the summer transfer window for £116 million, is showing encouraging signs after a tough start to life at Anfield.
"There's a very good reason why a club like us bought him," said Van Dijk. "He's an outstanding, world-class player, in my eyes, who can only become even better but it will take a bit of time.
"For him he has to stay level-headed. Don't get dragged into the outside world of when it's very good or very bad and don't get dragged into the numbers game.
"Nowadays there are a lot of eyes on you if you score goals or have an assist or keep clean sheets but it is also about what you see and the contribution you have for the team."