|Full name||Willian Klaus|
|Date of birth||11 January 1994|
|Place of birth||Dois Irmãos, Brazil|
|Height||1.87 m (6 ft 1 1⁄2 in)|
|Playing position||Centre back|
|2017||→ Internacional (loan)||14||(4)|
|* Senior club appearances and goals counted for the domestic league only and correct as of 16 May 2018|
Born in Dois Irmãos, Rio Grande do Sul, Klaus represented Grêmio, Internacional and Juventude as a youth. He made his senior debut with the latter on 12 March 2015, starting in a 0–1 Campeonato Gaúcho away loss against União Frederiquense.
Klaus became a regular starter during the 2016 campaign, as his side achieved promotion from the Série C and reached the quarterfinals of the Copa do Brasil. His first senior goal came on 21 April of that year, the second in a 2–0 home win against former club Grêmio.
- As of 18 December 2016
- One appearance in Copa FGF, four appearances in Supercopa Gaúcha
- "Juventude: Klaus, um zagueiro de números" [Juventude: Klaus, a defender of numbers] (in Portuguese). Rede Esportiva. 10 March 2016. Retrieved 20 April 2016.
- "Na raça, enfim, a primeira vitória!" [Through effort, finally, the first win] (in Portuguese). União Frederiquense. 12 March 2015. Retrieved 15 December 2016.
- "Grêmio sofre sem Geromel, leva 2 a 0 e se complica na semi do Gauchão" [Grêmio struggle without Geromel, lose by 2–0 and get into trouble in the Gauchão's semi] (in Portuguese). UOL Esporte. 21 April 2016. Retrieved 15 December 2016.
- "Após entregada de Ernando, Inter oficializa contratação de Klaus" [After Ernando's fluke, Inter turn official the signing of Klaus] (in Portuguese). Globo Esporte. 19 January 2017. Retrieved 30 January 2017.
- Klaus at Soccerway. Retrieved 20 April 2016.