Knapman, who was last season’s top scorer in South West Division One, went off injured after heading her team into the lead last week against Milton Keynes in the League Cup.
The Pilgrims will travel up to Kent on Saturday for their third league match of the 2018-19 campaign.
They opened up with a 4-3 win at Milton Keynes, who they also beat 4-2 last week at home in the cup, before slipping to a 3-0 defeat to Chichester City.
Their opponents this weekend, Gillingham, have a draw and a defeat to their name so far in the league.
As well as Knapman, Argyle are still unable to call on new signing Jessica Jones, whose international clearance has still not come through.
Jones was playing professionally for Calgary Foothills in the United Women’s Soccer League.
She is an England under-20 international and has returned to Devon to continue her career in nursery education.
Argyle’s development team will play local rivals Plympton on Sunday in the South West League Western Division.
They finished as runners-up last season and made an impressive start last weekend with a 6-3 win at Bude Town. Last season’s top scorer Gabi Alphous and 16-year-old Nicola Champion both scored twice in that game.