United's Premier League title defence is in tatters, with seven defeats in their first 22 matches seeing them sit seventh in the table.
They are already 14 points behind table-toppers Arsenal, and despite Saturday's club-record acquisition of Juan Mata - which took their spending this season beyond £65 million - from Chelsea, a title push looks highly unlikely.
And Moyes admitted he is "disappointed" with the club's start to the season, and says several players are on their last chance, promising to make more big-name signings like Mata.
"I am not going to accept it," Moyes said.
"I'm disappointed that we're not in a much stronger position. I'm disappointed with how we have played.
"I will ultimately take the rap for that, but what I will do is make it right.
"I'm going to get better players in. There will be more.
"I don't think there will be more in January, but it will change. I have said many times that I have given every player here the opportunity to play and show what they can do.
"We have nearly done that now."
Moyes reiterated his view that Mata was the first of many signings, acknowledging the size of the task at hand as he looks to improve United's fortunes.
"A couple of new signings isn't all that's needed," he added.
"There's a bigger job to be done, but you have to start somewhere."
