Sigurdsson joined the Swans for a second spell from Tottenham Hotspur for an undisclosed fee in July 2014.
Nicknamed the Ice Man, Sigurdsson spent two seasons at White Hart Lane, scoring eight goals in 58 top-flight appearances for the London club.
The midfielder is no stranger at the Swans having scored seven goals in 18 games during a successful loan spell in the club’s debut Barclays Premier League campaign in 2011-12.
Sigurdsson started his career with Reading, including loan moves with Shrewsbury Town and Crewe, before heading to Germany to join Hoffenheim.
His successful loan spell with the Swans then caught the eye of a number of clubs, with Spurs paying £8.8million for his services in July 2012.
After two years in North London, Sigurdsson returned to the Liberty. In his first full campaign with the Swans in 2014-15, the Icelandic international impressed by netting seven times in the league and nine times in all competitions.
And the following campaign was even more successful for him as he scored 11 goals and won three club awards - Supporters' Player of the Year; Players' Player of the Year and Away Player of the Year.
On the international stage, he starred for Iceland as they reached the last 16 of Euro 2016, with Sigurdsson scoring once during the tournament.