Ajax have announced the signing of Southampton's Dusan Tadic on a four-year contract for a fee of €11.4 million.
Tadic, with Serbia at the World Cup, joined Southampton from Twente in 2014 and will return to the Netherlands after four seasons.
The transfer fee for Tadic could increase to a maximum of €13m based on certain conditions.
To replace him, Southampton have lined up Basel's Mohamed Elyounoussi for a fee in the region of £16m, sources have told ESPN FC.
Elyounoussi, 23, scored 13 goals and provided 17 assists in 44 appearances for Basel last season, including a goal in the 2-1 win over Manchester City in the Champions League in March.
Sources also told ESPN FC that both Southampton and Everton have launched bids for Borussia Monchengladbach defender Jannik Vestergaard.
Vestergaard is currently with Denmark at the World Cup, where he has yet to feature.
The 25-year-old has spent the last eight seasons in Germany with Hoffenheim, Werder Bremen and Monchengladbach, and West Ham United and Watford are also considering moves for him.
Information from ESPN FC's Peter O'Rourke was used in this report.