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Liverpool have established a 22-point advantage over reigning champions Manchester City at the top of the Premier League this season, with only 10 fixtures remaining.
Jurgen Klopp's men have set unprecedented new standards of consistency, dropping points on just two occasions, while also attempting to defend the European crown they claimed last year.
However, the Reds have taken their foot off the gas somewhat since returning from the winter break, with a Champions League last-16 first-leg defeat away to Atletico Madrid marking the beginning of their troubles.
That result was followed up by an unconvincing win over West Ham, before Liverpool surrendered their unbeaten top-flight record by losing 3-0 to Watford at Vicarage Road on Saturday.
Liverpool will almost certainly still wrap up a first league title in 30 years and a second successive Champions League triumph cannot yet be ruled out, but Brown does not believe they can be measured against United's 1998-1999 outfit.
"This Liverpool team is a very good team," the former United defender told talkSPORT .
"They've totally dominated in the league this season but until someone actually does the treble there are no comparisons to make.
"It's not even a question to me at all! You can only compare when a team has actually done it. Winning the treble is such a difficult thing to do."
United have fallen well behind Liverpool in English football's pecking order in recent times, with 37 points currently separating the two sides in the top-flight standings.
Ole Gunnar Solskjaer has very different goals for the Red Devils, who are currently chasing a top-four finish along with success in the FA Cup and Europa League.
The Norwegian boss has faced plenty of criticism since taking over at Old Trafford, but Brown believes he is putting the foundations in place for future success.
"Ole's a top man...I think he's gone the right way about building the team," he added.
"Ole brought in some signings at the beginning of the season in Harry Maguire, Aaron Wan-Bissaka and Dan James and in January Bruno Fernandes and Odion Ighalo have come in and I think it's just starting to come together.
"I know Bruno has only been there a short time but you can see the confidence he brings to the team. He's a player that wants to do well and he's got the ability to do it. You can see players running in now and I think that's a big step forward.
"The club can see what Ole's doing and they'll get behind him and support him."