The Brazil left-back will become a free agent next summer after turning down an extension with Porto.
And the Portuguese club are now lowering their demands so as not to lose Telles for free next summer.
That is £9.2m less than their original asking price of £27.7m.
The drop in price helps United as they are looking to spread their funds across multiple positions.
Ole Gunnar Solskjaer wants a left-back, centre-back and winger to round out his squad ahead of their opening Premier League fixture next weekend.