Midfield blow for Kings
Klaasen suffered a hamstring injury which saw him absent during the 12-26 defeat to Welsh side on Friday.
The centre will be on the sidelines for a lengthy period of time and has been sent home to South Africa.
Jacques Nell will join the travelling squad as a replacement for their upcoming match against Leinster.
Stephan Coetzee, who dislocated a finger after coming on as a replacement against Ospreys, was showing no ill-effects.
While prop Dayan Van Der Westhuizen, who missed the match on Friday due to an ankle injury, had responded well to treatment and will also be available for Leinster clash if needed.
๐ That was hard work ๐ but @Jeff_Hassler secures a bonus point for @ospreys as @SouthernKingsSA's sturdy defence eventually gives way with 14 men on the field.#OSPvKIN #GUINNESSPRO14 pic.twitter.com/9BVwDUSomn
— PRO14 RUGBY (@PRO14Official) February 16, 2018