Ferguson had indicated at the unveiling of Robin van Persie on Friday that the Dutchman's arrival from Arsenal was likely to be the last bit of business this summer.
However, Ferguson has revealed he is confident he would get the backing of the club's owners, the Glazers, if he wanted to make another foray in the transfer market.
"I think that is maybe it [in terms of signings this summer]," Ferguson told MUTV. "Maybe in one other position.
"We have spent a big amount of money and, if I need to go to the owners, I am sure they would say 'yes'. But it's only if a certain player would become available."
Ferguson revealed earlier this summer he could be in the market for a new left-back with United short of cover and he has been linked with a move for Everton's Leighton Baines.