Brereton Diaz spent the latter half of the previous season on loan with Sheffield United, netting six goals across 14 appearances in the Premier League.
Southampton has been in search of a new forward following Che Adams’ decision to join Torino this month after declining new contract proposals from the Saints.
Brereton Diaz kicked off his career at Nottingham Forest, then moved to Blackburn Rovers, where he found the net 47 times in 177 outings over five years.
He switched his international allegiance to Chile after progressing through England’s youth system and made his international debut in 2021.
The 25-year-old participated in Chile’s three matches during the Copa America last month, as La Roja finished third in Group A, trailing behind Argentina and Canada.
He joins summer acquisitions Adam Lallana, Taylor Harwood-Bellis, Charlie Taylor, Ronnie Edwards, Nathan Wood, Yukinari Sugawara, and Flynn Downes as the Saints gear up for their Premier League return following victory in last season’s Championship play-offs.
