The Blues only managed a goalless draw against Everton while United managed to beat Portsmouth at home.
United are now six points ahead of Chelsea and does also have a game in hand.
Hiddink declared: “Mathematically, there may still be a chance. But we have to be realistic.
“We said before the match that the two teams chasing Manchester United must not waste any more points if we were to stay in the race.
“But the fact is we have lost two points here and now must focus on the other two roads in the Champions League and FA Cup.
“There was always more pressure on Liverpool and Chelsea than on United, because of their game in hand.
“All the players are disappointed after this result and we now have to focus on next week’s very difficult Champions League game in Barcelona.
“I will analyse this game and see how many of our players are in the overload zone. It is possible a few might now get a rest and play less in the league.”
