Simon Deli joined Slavia in January 2015 and launched his red-white spell as defensive midfielder. He played 13 games in midfield in his inaugural season for the club. In 2015/16 he moved closer to the goalkeeper and started playing in the centre of the defence. He made 28 caps, scored his first goal during a 4-0 win against Jihlava and helped Slavia to finish 5th and return to the European competitions.
A year later Slavia wit Simon Deli as one of the key players won the Czech championship and lifted the title after 8 years. Deli started to 25 games and scored one goal. After the unlucky 2017/18 season which saw him start to only 10 games because of a long injury, he made his top performances during 2018/19 season which ended with the Czech double and the UEFA Europa League Quarter-final.
“I remember my very first game at Eden. But I would stress the home game against Chelsea when I was Slavia captain, and the double just before I left for Belgium. Those moments I will remember forever,” Deli said after his 100th start in Teplice.
Simon Deli returned to Slavia from Club Brugge on loan till the end of the 2020/21 season. With his starts against Příbram, Pardubice and Teplice he reached 100 league games in red and white.