The Paraguay international is on his way out of Spain after his club agreed a fee with the Russian outfit, who will end their long-winded search for a new striker
The 27-year-old is set to pen a five-year contract with the Russian Premier League club, worth €2.4 million per annum, despite interest from Getafe and Espanyol.
A statement on Hercules' official website read: "Hercules have reached a preliminary agreement with the Russian club Rubin Kazan for the transfer of Nelson Haedo Valdez. The details of the transaction will be posted during the week."
It marks an end to Rubin's summer-long search for an international striker after failing to land the likes of Klaas-Jan Huntelaar and Diego Milito during the window.
Valdez scored eight times in 25 appearances in La Liga for the Alicante-based outfit last season, who suffered relegation to the Segunda Division. He also featured in this year's Copa America for Paraguay, in which he scored in their 2-2 draw with Brazil during the group stages.