The 22 year-old is currently playing with Albacete and is wanted by Barca as a replacement for Abel Ruiz. Ruiz is set to leave in January, with Valencia keen.
Manaj will join Barca B on-loan with the option to sign permanently.
The young striker was snapped up by Albacete from Inter Milan for €2m and has caught the eye of Barca scouts.
This season, Manaj has scored twice in nine games.