McNamara's men had earned much praise for their attacking football during a six-match winning streak, but defeats by St Mirren, St Johnstone and at home to Aberdeen have brought run to a shuddering halt.
United play a confident Hibernian team on Sunday, who arrive at Tannadice on the back of a 2-1 derby victory over Edinburgh rivals Hearts.
McNamara said: "My thoughts on Sunday's match are that we need to win it. We are at home but I think we need to play a lot better than we did against Aberdeen.
"We will need to pass the ball a lot better and hope that the pitch has not taken too much of a battering after the heavy rain during that match on Wednesday.
"We felt the Aberdeen match was a chance to bounce back after the St Johnstone defeat but we didn't take it. The Hibs match is another chance for us to do that.
"We are hurting at the moment but we must dust ourselves down and get ready for Sunday."