Their former right-back has been a consistent supporter of ex-United teammate Ole Gunnar Solskjaer, but that may have finally changed.
The Sky Sports pundit was shell-shocked by his team's performance as they slumped to a 4-0 half-time deficit for the first time ever in the Premier League.
Goals from Naby Keita, Diogo Jota and a Mohamed Salah hat-trick condemned United to a horrifying 5-0 loss at Old Trafford, with Neville as shocked as anyone.
"I didn't think it would ever get as bad as that today," Neville said.
"That's as bad as it's been in this fixture in terms of distance between the two clubs for maybe 40 or 50 years.
"It's always been a tight game more often than not, but today that was a shocker."
United have had their heads kept above water largely by moments of individual brilliance, such as Cristiano Ronaldo's late winner in a 3-2 victory over Atalanta in the Champions League midweek.
But performances have been below par according to Neville, with this sort of result always on the horizon.
"The timing of the game couldn't have been worse," he said. "It's been building now for a few weeks with what I call half-decent displays and as soon as they play a decent team they've been obliterated, pulled to pieces and dismantled.
"I didn't think they would play like that because they would flick a switch, but you can't flick a switch in football."
United's defence was torn to shreds in the first half, with a disorganised team all over the place.
The lack of control later led to a Salah hat-trick, the first from an away player at Old Trafford since 2003 when Ronaldo netted a treble for Real Madrid in the Champions League, with Paul Pogba then seeing red for a nasty challenge on Keita.
"Manchester United's players got outrun," Neville explained. "They're one of the lowest running teams in the league - we know that from the stats we see week in, week out - and there's nothing worse than being one of the lowest running teams and being easy to play against, but they're both.
"That's a poor reflection on the manager, the staff and the players."
talkSPORT commentator Perry Groves was just as shocked by what he was watching, singling out Harry Maguire as Liverpool blasted to a 2-0 lead.
"When you play Liverpool you've got to have cohesion, synchronicity… [Victor] Lindelof dropped off, Luke Shaw doesn't know where he's going and Harry Maguire is lost," Groves said.
"He's just wandering around in the middle of the pitch, he doesn't know what to do.
"When they pan over to Ole Gunnar Solskjaer he has that look over his face where he thinks 'I don't know what to do.'
"If Liverpool keep playing like this and go for the jugular, this could end up four or five."
"Look at the structure at the back for both goals… you tell me there's shape there because I can't tell you!"