Nicolas Anelka maintains Chelsea's season is very much still alive despite falling further behind in the Prem title race.

The Brazilian, though, has vowed to improve the performances and insists the remedy does not lie with simply bringing in new faces during the January transfer window.

Chelsea head to Southend on Wednesday night (Thursday AEDT) for their FA Cup third-round replay in search of a first win since Boxing Day - where defeat would provide both a massive upset and heap more pressure on Scolari.

However, Anelka, who came on as a second-half substitute at Old Trafford, insists all is not yet lost.

"The fans have been frustrated by our recent results, which is logical," he said.

"As far as the players are concerned, we have not been happy with some of our games.

"The positive point is that we are still on course for the treble.

"We understand it's going to be massively tough, but everything is possible."

United took the lead in first-half stoppage time through a far-post header from Nemanja Vidic, with goals from Wayne Rooney and Dimitar Berbatov ensuring there was no way back for Chelsea, now four points adrift of table-toppers Liverpool and only one in front of Sir Alex Ferguson's men, who have two games in hand.

Scolari accepts Chelsea - with captain John Terry available again yesterday following a three-match suspension - must recapture their defensive unity.

"Losing goals at set plays is not something we accept. We train very hard to try and stop it happening," he said.

"Set-pieces have been a problem. In the first 15 or 20 games we were fantastic. I don't know why it has changed.

"Maybe I need to change the system because something is going wrong. It is my responsibility."

Defender Ricardo Carvalho feels the players must stand up and be counted.

"We have to mark our men and this time we didn't mark our men, and goal after goal it is getting worse for us," Carvalho told Chelsea TV.

"Our mistake was the corner and we conceded a goal in the last minute of the first half.

"After that it was difficult to react, we tried but the second goal killed us."

Midfielder John Mikel Obi has issued a rallying call ahead of the cup clash with the Shrimpers.

"We are football players, top football players, and no one likes losing," he said.

"You get things going wrong like this and it depends how we get on with it and try to fix everything right now.

"In this time we have to show our strong character, remain as a family and get things right."

Mikel told the official club website: "It helps to have a game so soon, it is a good game to go out and make sure we win."