The midfielder spent the 2004-05 campaign with Southampton but moved to Panathinaikos following the Saints' relegation from the Premiership. He started only 12 league games for Southampton following his £500,000 switch from Halmstads in July 2004. The versatile Nilsson is usually used on the right side of midfield but can also play in defence. He scored twice on his international debut in the 3-3 draw against the Czech Republic in 2002 and played in every minute of Sweden's run to the quarter-finals at Euro 2004. Nilsson starred for Panathinaikos in the Greek side's 2005-06 Champions League campaign.