Liverpool are fourth in the Premier League table, three points and three places ahead of their fierce rivals and have won their last five matches in all competitions.
United, in contrast, have only won three of their last seven fixtures across all competitions and can ill afford another loss in the league.
The Red Devils were busy in the transfer market in the summer, signing defender Eric Bailly, midfielders Paul Pogba and Henrikh Mkhitaryan and striker Zlatan Ibrahimovic, while the likes of Tyler Blackett, Will Keane and Paddy McNair were allowed to leave the club.
But Scholes said Mourinho was not decisive enough in the summer and claimed that he still does not know what his best team is.
"He was not ruthless enough in the off season," the ex-England international was quoted as saying by the BBC.
"There is so much confusion about who should play.
"What I saw of Mourinho at Chelsea, he had 13 or 14 players who played every week. He never rested players even in the League Cup or whatever competition he was in.
"With United it is still a settling-in period – it is going to take a bit of time for them to knit together and see what they are about.
"Is there an identity to the team yet? I don't think there is."
In contrast, Scholes noted that Jurgen Klopp had been in charge for a longer time at Liverpool and had had more success in instilling his ideas at Anfield.
"You can see Jurgen Klopp has stamped his way of playing football on the team," he stated.
"There is a definite way about them. You know how they are going to play. They are going to be quick, they are going to try to take the ball off you and try to score goals by flooding the box.
"If you were betting, you would be betting on Liverpool," Scholes added.