The Paris Saint-Germain forward has agreed terms with Los Che and is expected to replace the newly-departed Aritz Aduriz, who has been sold to Athletic Bilbao
The 25-year-old, who has eight caps for France, has reportedly agreed personal terms with the La Liga outfit after growing frustrated at the lack of playing time in the French capital.
However, PSG are understood to be unwilling to sell Gameiro until they find a suitable replacement for the forward.
The Parisian club had to stave off strong interest from Valencia last summer to sign the forward for an estimated €11 million from Lorient, but it appears he will now be moving to the Mestalla in a cut-price deal.
Gameiro's arrival will be a welcome boost for new Los Che boss Mauricio Pellegrino, who this week sanctioned the sale of Aritz Aduriz to Athletic Bilbao.