Former All Blacks lock and Crusaders coach Todd Blackadder says Sonny Bill Williams' days in the black jersey could be numbered after unconvincing performances while on the northern hemisphere tour.

Former Crusaders coach and current Bath Rugby coach Todd Blackadder. [Photo: Getty]

Williams hinted yesterday that he may continue playing after the 2019 Rugby World Cup in Japan.

This year the 33‑year‑old cross‑code star had a disrupted season, where he injured his knee against France in the All Blacks' June series and then suffered a shoulder injury against England last month.

Blackadder told The Rugby Paper that the All Blacks selectors will have a lot to discuss about Williams' future in the team.

Blackadder coached Williams at the Crusaders in 2011 and has been a staunch Williams supporter in the past.

Blackadder said the northern hemisphere tour gave the All Blacks a good opportunity to tweak their game plans ahead of the Rugby World Cup.

Blackadder is now the coach for English club Bath.

[Source: TVNZ]