Two months on since arriving in England, the young centre-back is yet to make his debut for his new club owing to fitness challenges.
“Sali is still building up to being part of the team,” Southampton manager Hasenhuttle told pressmen in his team news on Friday ahead of Sunday's tie against Everton, his club's official website reports.
“He has been in team training this week, completely, but we have to be careful with him.
“There were some bigger issues we had with him and these issues will last a little bit longer, so we have to take care of him, but he is coming back.
“Maybe it takes one more week and then he is able to play, but we will give him all the time he needs to solve his issues.
“We knew it was not a short-term project. It is a long-term project, he is a good guy, and I’m sure that he will help us in the future.”
Although Salisu put pen to paper for Southampton in August, he joined the club's pre-season training in September, precisely in the week of the club's first game of the Premier League campaign.
"It may take a few more weeks, maybe [to break into the starting set-up]. After the next international break [in October], I hope to have him in the first eleven. He has a good drive and is a very ambitious guy," Hasenhuttl told Hampshire Live in September.
"He is working hard on his fitness at the moment after a long break from injury and there are a few issues we must work on but you can see his physicality.
"The potential he has is amazing and he wants to learn quickly. He is exactly the type of player that we need to have here.
"We have very clear and strict limits on any transfer we make. We have to have a player that really likes to come to us for money we can spend.
"If we find such a player then I am sure he will enjoy it and develop very quickly when he is with us.
"He will not be a short-term project, he will be more of a long-term project. Therefore I think he was a fantastic transfer."
After five rounds of matches, Southampton are 12th on the league table.