Doherty, who has scored in his last three appearances, picked up his fifth booking of the season against Huddersfield last weekend and will miss out through a one-match suspension.
Askou is still out with the foot injury which forced him to miss the 3-0 win over the Terriers so Michael Nelson is the only fit centre-half at Carrow Road.
One contender to fill in, Michael Spillane, remains sidelined with a hamstring injury so Russell Martin could move across from full-back to deputise.
Korey Smith is also out with a thigh problem so Tom Adeyemi will continue in midfield and Declan Rudd (knee), Luke Daley (thigh) and Owain Tudur Jones (groin) are all out.
