The 25 year-old has been thriving in the Dutch Eridivisie for many seasons now and only now will he make his next move in his career with a move to the EPL.
It is believed that the attacking midfielder will join the club for a fee around the 9.6 million pounds mark and would be a very cost effective solution to Lallana if he continues his great form outside of the Netherlands.
But Tadic will not be the only player to make the move from the Netherlands to Southampton with Koeman eyeing a host of names to help rebuild the side from the Eridivisie as he coached Feyenoord for a number of seasons and hence knows many of the players.
The Serbian international scored 16 times and provided 14 assists in another stunning League season where he helped the club to a third placed finish.