Ole Gunnar Solskjaer’s side have lost two out of their first three league games and entered the international break off the back of a 6-1 defeat at home to Tottenham.
United were given an extra week to prepare for the new season following their Europa League mini-tournament in August, but Solskjaer’s players had just one friendly before the Premier League began.
And Lindelof believes some of United’s players began the season still short of rhythm and fitness.
‘It hasn’t been the best start for us in the league, I don’t know what it’s all about. If it’s because we played for a long time in Europe [in August] and didn’t get the time off we usually get, it is difficult to answer,’ Lindelof told Aftonbladet.
‘We probably had one or two weeks together before the league started and we haven’t got to the level we’ve wanted.
‘But I think after this international break, a lot of players are back and ready to perform at the level we can.’
Lindelof, who is currently with Sweden’s national team, also dismissed claims that United are concerned over his levels of match fitness.
‘Not for me personally. I have been set to play two matches in this selection [for Sweden in October],’ said the Swede.
‘We can talk sometimes when it comes to certain selections.
‘Like the last selection, I had a talk with Janne before and we agreed that I would only play one match because I felt that the body did not agree to play two games. But for this selection there has been nothing.’