Senegal forward Sadio Mane, have been signedfrom Austrian champions, Red Bull Salzburg for £10m.
The 22-year-old Southampton import, who scored 45 goals in 87 games during two seasons in Austria, can play on either wing or centrally, Saints manager, Ronald Koeman, said.
Southampton also completed the season-long loan signing of Belgium defender Toby Alderweireld from Atletico Madrid.
Alderweireld helped Atletico win Spain's La Liga title and reach the Champions League final last season.
The 25-year-old, who can play at either centre-back or right-back, has won 37 caps for his country.