The 50-year-old admits his side's form may not drastically improve and believes the club need to sign players who will make an instant impact at Old Trafford
The Premier League champions have secured seven points from five games, which is the club's worst start to a campaign in nine years.
United will be looking to bounce back from their loss at the Etihad Stadium on Sunday with a victory in the Capital One Cup against Liverpool on Wednesday, but the 50-year-old admits his side's form may not improve straight away.
"Not for a minute did I think this Manchester United job was going to be an easy job," Moyes said.
"There will be days like we had on Sunday, and there might be more of them because we're in a period where there will be transition.
"There's a new manager for the players, and in turn there will be new players as well at different times, so obviously that will happen.
"It does mean I may have to take a few more blows, definitely. Maybe even more than that - maybe all season I'll have to take a few blows - but I knew this was going to be the case because I was taking over from a great manager and it was always going to take time for me to get my own ways and change things round a little bit.
"It doesn't mean big jobs but there will be some things. I think a lot of people thought Manchester United [won the title] last season but it was probably the form of other teams that was poor."
Following criticism over the club's lack of transfer activity in the summer, Moyes insists he has adequate squad depth for the season but admits United now need to sign players who will make an immediate impact at Old Trafford.
"I don't think it's actually the squad. I think we've got numbers," the United boss said.
"I think maybe where we've got work to do is bring players in, not for the squad, but to go right into the team, so that's the slightly different equation.
"It's not necessarily squad players we needed. We needed one or two who might have just gone straight into the team. But that will happen.
"Going back to that transfer window, we always said it was going to be a tough one and it was going to take a little bit more time."