Northants will be without Steven Crook, Richard Gleeson and Seekkuge Prasanna for T20 Blast Finals Day.
Sri Lanka spinner Prasanna, 31, has not been released by the Sri Lankan cricket board as he will be part of their one-day squad to face Australia.
Northants will play Nottinghamshire in the first semi-final of Finals Day at Edgbaston on Saturday.
Meanwhile, 26-year-old all-rounder Josh Cobb has signed a new three-year deal with Northamptonshire.
Cobb, who moved to Wantage Road in 2014, is Northants' second highest run-scorer in the T20 Blast so far this season with 377 at a strike rate of just over 124.