Cesc Fábregas has admitted Arsenal were "scared" of losing to Manchester United at Old Trafford last Monday and that they fear defeat in major fixtures.

Arsenal lost 1-0 to a Park Ji-sung header to continue a dire run against United, who beat them home and away in the league last season. Arsène Wenger's side have also lost their last four league games against Chelsea, the reigning champions.

"They [United] were more aggressive than us," Fábregas said. "They have the belief that comes from not losing at all [in the league] this season. That gives you a lot of help mentally. I'm realising more and more that football is all about confidence and mentality. Sometimes you do the right thing but, if people tell you it's not right, you start believing it, even though you were right at first.

"I think the difference on the night was that we were scared of losing but they were not scared of winning. That was a big difference that played in our heads. Sometimes we seem scared of losing these big games – we don't really go for it and we're tempted to drop back and see what the opposition do. We look to see if we are capable of beating them by what they are doing and how good they are on the day, instead of us going forward, causing them problems and dominating the game ourselves."

Wenger admitted his side had been tense. "We looked a little nervous at Old Trafford. We put a bit too much pressure on our shoulders because we were so intent on winning a big game and as a result we didn't turn up with the kind of performance we can produce."

Arsenal are two points behind United, who have 34 points and a game in hand. Yet with Manchester City level with Arsenal and Chelsea a point behind, Wenger believes the title race is unpredictable. "This championship remains very open. Don't forget that we have played at United, at City, at Chelsea and at Liverpool, so we are in a strong position. Now the rest of the season will be decided on how much we've learned, how much we improve and how much confidence we can take from our performances so far."

Arsenal play Barcelona in the last 16 of the Champions League, having been defeated 6-3 on aggregate by Pep Guardiola's team in the quarter-finals last year. But Wenger said: "We want to qualify, to knock them out, rather than worrying about avenging last year's defeat."

Wenger is content regarding injuries. "Overall the situation looks quite positive. Abou Diaby is back in full training. Cesc Fábregas and Robin van Persie have had more minutes on the pitch and are getting better and better. We think Thomas Vermaelen can return in January."