Louis van Gaal feels he will need far longer to turn Manchester United's fortunes around despite completing the pre-season with six wins out of six.
United rounded off their schedule of pre-season fixtures with a 2-1 win over Valencia on Tuesday, giving the Dutchman, who took over after leading the Netherlands to third place at the World Cup last month, victory in his first match as Red Devils boss at Old Trafford.
They now face Swansea in their Premier League opener at home on Saturday but van Gaal is unsure whether Jonny Evans, Luke Shaw and Antonio Valencia, who sat out Tuesday's match through injury, will be available.
With those three sidelined, Van Gaal had Phil Jones, Chris Smalling and Tyler Blackett at centre-back, with Ashley Young and Reece James playing as wing-backs and Michael Keane the only defender on the bench against Spanish side Valencia.
Left-back Shaw and midfielder Ander Herrera have been the only new signings so far this pre-season, although United are widely reported to have made a Â£16 million offer for Sporting Lisbon's 24-year-old Argentina centre-back Marcos Rojo.
Including a goalless draw against Inter Milan, which they went on to win on penalties, United have record victories over LA Galaxy, Roma, Real Madrid and bitter rivals Liverpool during their pre-season campaign.
However, van Gaal believes the win over Valencia, secured with an injury-time goal from substitute Marouane Fellaini, was the worst performance yet as United get to grips with his ideas.
And he warned fans not to expect too much early in his United reign, with the club looking to bounce back after finishing, by their standards, a lowly seventh in the Premier League last term, with David Moyes sacked as manager before seeing out his first season in charge despite being retired boss Alex Ferguson's chosen successor.
- 'Big pressure' -
"It was fantastic," said van Gaal of the way he was greeted by United's fans.
"Coming on the pitch and they are shouting and screaming your name, but there's also big pressure because they expect a lot and you can't change everything in three or four weeks and the players can't change either.
"We have to wait and see and develop and we need time, but we have won every game to now and that's fantastic when you see our opponents.
"We have great confidence to play against Swansea.
He added: "I think we have a lot of injuries now and we can't forget that.
"Jonny Evans was injured, Shaw was injured and Valencia was injured and they are three defenders.
"We have to wait and see if they can play on Saturday but the main thing is that we have won in spite of playing our worst game."
Wayne Rooney missed a penalty against Valencia in the first half before Darren Fletcher's deflected effort put the hosts ahead just after the break.
Rodrigo Moreno pulled one back when Tom Cleverley failed to clear Pablo Piatti's free-kick.
But in added time at the end, Fellaini, whose every touch had been ironically cheered by home fans, controlled a long ball and rolled into the net for his first United goal since joining from Everton a year ago.
Van Gaal wants to see more from his team in the weeks ahead," saying: "The boys want to show our capacity what we have shown in the United States too much and that is also not good.
"We made a lot of wrong choices, wrong passes and we didn't press too much but in spite of that I think Valencia is a very good team, very comfortable on the ball so it is not easy to press.
"But in spite of that we have dominated the game, only in 15 minutes in the second half we are not dominating, I think, and at the end we are the winner because we are fighting until the last minute and that is also a good signal, I believe."