"You never know what will happen but if we play like we did today for the next three or four games we will not win," the 60-year-old Brazilian added.
"But now is the time for me and the players to think about the future. We can lose everything or we can be men and we can improve."
Second-placed Chelsea have won only one of their last five league games and were easily overpowered by United, who are now only one point behind them in third spot, with two games in hand.
Didier Drogba got the nod ahead of Nicolas Anelka to start up front on his own and while he helped Chelsea compete physically in the first half, Nemanja Vidic's opener just before the break preceded a woeful second-half display.
"Manchester United were better than us," added Scolari. "We were thinking about winning the game.
"Our performance for the first 45 minutes was very well but then we conceded a goal and that changes the game.
Inter Milan boss Jose Mourinho was eyeing up United at Old Trafford
"After this goal they could play more freely. We tried to put more players in front and we give them the space they want to play.
"Now we need to think about the result, what happened to some players, what happened from set-plays and now we have to think about the future." Despite his side's poor form and having recently off-loaded defender Wayne Bridge to Manchester City, Scolari maintained he remained happy with his current squad.
"We don't need more players," he said. "I don't think they will arrive and I don't want them anyway. This is my squad and I will improve them."
Scolari was also adamant the presence of Chelsea's former boss Jose Mourinho - now manager at Inter Milan - at Old Trafford had not added any pressure on him for Sunday's game.
"Mourinho came here to watch Manchester United for the Champions League match next month," Scolari said. "That is normal. He is an intelligent man. He didn't come to tell me he loves me."
Following their win, Manchester United manager Sir Alex Ferguson called on his players to make the most of the momentum they are building as they chase league leaders Liverpool, who are five points ahead of the Old Trafford outfit but have played two more games.
United could go top if they beat Wigan at home on Wednesday and Bolton away on Saturday, with Liverpool not playing Everton until Monday evening.
"After watching Liverpool draw on Saturday, we got exactly the result we needed," stated Ferguson.
"But we've got some tough games coming up now. We've got Wigan, who are playing fantastically well at the moment, on Wednesday and then Bolton away, which is also a tough game.
"If we do our jobs right and win our two games we could be top of the league on Saturday.
"It is down to us now because it is something we want. We want to look at that table on Saturday and be top.
"So there's a lot of interesting games to see in the next few weeks. January, as I've said, is a big month for us."
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