Boston United skipper and leading scorer out of starting XI, striker battling tonsilitis to face Hednesford Town
Defender Shiels failed a fitness test at Keys Park after picking up an injury in training on Thursday and will be replaced by Lewis Gibbens in defence.
Thewlis, who has netted eight times for United this campaign, will start on the bench as he struggles with a groin problem.
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Hide AdStriker Dominic Knowles will start despite being prescribed antibiotics as he battles tonsilitis.
Craig Elliott has made four changes to the side which lost 2-1 at Darlington last Saturday, Gibbens, Ashley Jackson, Andi Thanoj and Martyn Woolford replacing Shiels, Thewlis, Nicky Walker and Ben Middleton.
Kick off will be at 3pm.
UNITED: Crook, Jackson, Whittle, Platt, Gibbens, Ainge, Thanoj, Abbott, Knowles, Woolford, Rollins; Walker, Willis, Adebayo-Smith, Thewlis, Tuton, Middleton, Wafula.
REF: Dale Wootton.