Oxford had been hoping to agree a deal with Reading to take 33-year-old Viveash to the Kassam Stadium permanently, however, the two clubs have been unable to agree terms.
Alan Pardew has made it quite clear that Viveash is not in his plans for the future, Adie Williams and John Mackie are his first choice defensive partnership.
Adi will begin his second month on loan with the U's shortly, the clubs still hope that they can eventually agree a permanent deal.
Pards told readingfc.co.uk: "It's disappointing that we've been unable to agree a pemanent deal.
"Adi's been terrific and we've bent over backwards to let him go back for another month with a view to it becoming permanent. Bearing in mind his personal situation, I hope that is the case."