Since talks began for Torres, City have been trying to use Herrera as a chip to bring down the price.
And while Valencia are keen on Herrera, owner Peter Lim wants any deal to be separate from the sale of Torres.
Valencia would like the money from Torres in their pocket before making any firm decisions on signings.
City could let Herrera, a 2017 signing from Atlético Venezuela, join Valencia on loan with an option to buy.
Granada also have an option to buy but their financial situation makes it avery difficult.
City value Herrera between €15m and €18m following his impressive loan spell at Granada.