The Wearsiders held talks with the 22-year-old last Friday after they and another club were given permission to speak to him.
However, Nugent went away on holiday afterwards to recover from his exertions with England at the European Under-21 Championships, and his suitors were left anxiously awaiting his return.
Quinn said: "We are one of two clubs, we believe, who have agreed, and he has gone away on holiday to think about it.
"We hope he will come back with the right decision. We will just have to wait and see.
"Would it be 50-50? It must be. The paper reports have been fairly accurate - not all of them - but we will see.
"He needs a bit of time. He has been playing football all the while.
"He came home and a day later, his whole career had to be decided.
"He has gone off to have a little break and we will see how he gets on with that."
West Ham, Portsmouth and Manchester City have also been linked with the former Bury striker, while talk continues of Everton, the club he supported as a boy, joining the chase.
Sunderland have already signed Reading full-back Greg Halford and Aberdeen skipper Russell Anderson for a total of £4million, but with Roy Keane having around £25million to invest, big things are expected on Wearside.
That was illustrated on Thursday night when hundreds of fans braved persistent rain over the Stadium of Light to attend the launch of the club's new away kit.
Season tickets sales have exceeded 30,000 after Quinn successfully took his quest to reconnect the fans to the club to the city's pubs and clubs.
However, the excitement has been tempered by the need for patience as the big breakthrough for which the supporters are hoping yet to materialise.
Reports have suggested the Black Cats had seen a £3million bid for Wigan full-back Leighton Baines rejected, and while there was no confirmation from the Latics, manager Chris Hutchings is confident the highly-rated England Under-21 international will remain at the JJB Stadium.
He told the Manchester Evening News: "Baines has told me he is happy to stay and I am certainly not looking to sell him."
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