The centre-back ended the 2023-24 season as Virgil van Dijk's first-choice partner, and he once again got the nod over Ibrahima Konate in last weekend's clash with newly-promoted Ipswich Town.
However, Quansah was hooked at half time after Liverpool faced a barrage of Ipswich attacks in the first half, as Konate and Van Dijk saw out a 2-0 victory at Portman Road.
It was initially suspected that Quansah had picked up an injury in the first 45, but Slot subsequently confirmed that the change was tactical in nature, as he believed that the youngster lost too many duels last weekend.
Konate was therefore always expected to come back into the first XI for the visit of Brentford to Anfield on Sunday, and speaking in his pre-game press conference, Slot revealed that Quansah was now a fitness doubt after picking up a problem in training.
Slot: 'Quansah reacted how I expected him to'
"In a way you would expect a player to react. I spoke to him immediately after the game, I spoke to him the day after on Sunday and at the end of that conversation he asked if he could train on the Sunday," Slot said.
"Normally he should have done recovery, [but] he wanted to train. Unfortunately, I think it was Tuesday that he picked up a bit of an injury, so he couldn't train on Wednesday - let's see if he can train today.
"He reacted in a way every player should have reacted. I don't think there was that much into it, although maybe the language was a problem because what I said was he did not lose every duel - but he lost one or two important ones, and one of them was just before half-time.
"From what has been told to me, it's like that I said he lost every duel - which he did not do, we as a team lost too many duels and he lost one or two as well. That's also what I said to the team the day after, it was not about Jarell [but] that we as a team didn't do well.
"In my opinion, the only threat at that moment from Ipswich was from [Liam] Delap and he won one or two important duels, [so] I was trying to get that strength out of their team by bringing in Ibou [Konate]."
While Konate appears to be first in line for promotion from the bench, Liverpool also have the long-serving Joe Gomez in their ranks, despite persistent talk of a possible move away for the Englishman this summer.
Slot responds to Gomez transfer rumours
Moves to Aston Villa or Newcastle United have been mooted for Gomez, who is reportedly valued at £45m by Liverpool and is open to leaving if the right opportunity comes along in the coming days.
However, Slot does not envisage Gomez leaving before the August 30 cut-off point and also hailed the Englishman's progress on the training pitch since Euro 2024, adding: "Yeah, it's [his head] been in the right place for three weeks. He's worked really hard since he came back, but he didn't play a lot at the Euros.
"When he came back in the first sessions he couldn't train the whole sessions, so we had to manage his load a bit. That was also the reason why he wasn't in the team last Saturday. But this week he had a good week in terms of load and how much he could do with the team.
"He's one of the players that I see new things from and learn things from what I see, also combined with other players. It's been a good week for him and for us until now. At this moment, I'm expecting everyone to be here. But like you know, everything can change."
Liverpool have sold two players to upcoming opponents Brentford this summer, allowing Fabio Carvalho to join for £27.5m before selling Dutch defender Sepp van den Berg to the Bees in a deal that could fetch up to £25m.