NewsJürgen Klopp's fitness update on Diaz, Nunez, Keita, Thiago and Gomez
The Reds will continue to take a patient approach with the No.23, who last made an appearance back in October away at Arsenal.
Meanwhile, Darwin Nunez is set to be available for Saturday's fixture with Pep Guardiola's team after recovering from the issue that saw him withdraw from international duty – but Naby Keita has been ruled out.
Offering an update on Diaz, Klopp told Liverpoolfc.com on Friday: "Yeah, we have to be patient but it's a massive boost anyway. It's just nice to have the boy around because he is a super energiser, super-positive impact with just being around.
"[His] English got slightly better, so he used the time to learn English, which is good.
"It was a super, super-strange and difficult season for Luis, it was the Arsenal game, what a situation that was when he got injured early in the season. It was a really bad day, by the way.
"So, we will see. In training everything looks fine but of course he's not in the squad for the weekend, there's no chance.
"Next week will be an important week for him; this week he was doing parts of training, next week I think most of the things he can do. Then we will see. Maybe [ready for] Arsenal but more likely Leeds after that."
Speaking at a press conference later, Klopp said: "Darwin couldn't train for two or three days this week still because of the cut he got against Real Madrid on his foot, but was yesterday then back in full training so he is definitely in contention.
"Yeah, we have [other injury concerns]. Naby is out, he came back with a muscle injury from the national team. We will see how long it takes but obviously the season is not too long anymore. There is a chance that Naby comes back but we have to wait a little bit.
"Thiago is in a good way but was not part of team training yet. I think if things go well he will probably be part of next week's team training, parts – [that] means we will see when he is back. Joe [Gomez] is fully back. Rhys Williams has a little bit of something.
"I think pretty much the rest is available; all back. We had a little bit stomach bugs here and there but [that] stopped two days ago so should be alright."
- Want to watch Inside Training? Subscribe to LFCTV GO now and get a month FREE using the code GOFREE23
Liverpool return from the international break with a trip to the reigning Premier League champions in a 12.30pm BST kick-off.
On the rest of the squad's condition ahead of the game, the Reds boss added: "Good but of course a few things are sore.
"These weeks after international duties are already super, super-special because the boys come back on different days; some came back on Tuesday, some on Wednesday, some on Thursday. Some came back yesterday – Robbo – but will be in training for the first time today.
"Then you have to manage intensity and stuff like this. But what I saw so far, looking good, they are all in a good mood and now we have to use that."
Reaction'Really pleased' - Matt Beard on cup win at Newcastle, Zara Shaw goal and rotation
Reaction'Very important' - Mo Salah reflects on Southampton 2-3 Liverpool
VideoSouthampton 2-3 Liverpool: Watch free highlights
ReactionArne Slot press conference: Southampton win, 'special' Salah and not getting carried away
NewsPlayer of the Match: Who was Liverpool's star man against Southampton?