Saphir Taider will reportedly leave Southampton less than a month after joining the club on a season-long loan from Inter Milan.
The 22-year-old moved to the Saints in a deal that saw Dani Osvaldo head in the opposite direction.
According to BBC Sport, the midfielder has not been able to adapt to Ronald Koeman's physical training demands.
It is believed that Taider will now join Sassuolo for the season, with the deal having no effect on Osvaldo's loan at Inter.