Saints have seen the likes of England internationals Luke Shaw, Adam Lallana and Rickie Lambert all follow former boss Mauricio Pochettino out of the south-coast club
However, Tadic, signed for what is believed to be in excess of £8million, is convinced Southampton can move forward next season
Tours striker Andy Delort is said to be on Koeman's radar as well as Lorient defender Bruno Ecuele Manga, who could be seen as cover for wantaway Dejan Lovren, who is determined to leave for Liverpool
"There was a lot of interest from other clubs, but I really wanted to finish (the transfer) and I could see Southampton was a good opportunity for me," Tadic told Southampton's official YouTube channel.
" I see this as a new step for me, so I want to show myself and to help the club
"I heard the club has a history, and I watched them last year and they played really good football, which is important because I am a football player and I like to play football.
"England has one of the best leagues in the world
English football is really good to watch, and it's going to be a pleasure to play here.
"I hope me and Southampton are going to have a good future."
Tadic is confident former Barcelona defender Koeman, who impressed while in charge of Feyenoord in the Eredivisie, can help develop his game
"Feyenoord have had a lot of success because of him, because he developed a lot of players and made them better," the 25-year-old added
"You always have a lot of respect for his teams because he is a Dutch legend
He is a really good coach and you can expect that his teams will play even better because of him, even if they don't have great quality.
"He is tactically really good, and it's very difficult to play against his teams."
Source : PA
Source: PA