Knights trail 26-24 from the first leg at Castle Park.
The winners will meet the winners of the tie between Ampthill or Coventry in the quarter-finals.
The two losing sides with the smallest aggregate margin of defeat from the five first round ties will also progress to the last eight.
Champions Ealing received a bye into the quarter-finals.
A fortnight ago the Pirates managed to inflict the Knights’ first loss in a competitive match at Castle Park since their defeat at the hands of Saracens last April.
The Pirates fielded a young team who were eager to impress and impress they did.
Their strength in defence was admirable and possibly stronger than when they played at Castle Park in the Championship.
However, they may have been helped by the 12 changes to the Knights team which appeared to disrupt the cohesiveness of Steve Boden’s side.
Saturday’s game is available for live streaming. Click HERE for more details.