Dungannon born Clucas, 22, signed for the Candystripes immediately following his trial appearance at Seaview.
Seanan’s former clubs include Preston North End and Bristol Rovers where he played with former Candystripe Mark McChrystal.
He has also played at International level for Northern Ireland at U21 level.
Meanwhile goals from Mark Timlin, Patrick McEleney, Philip Lowry and Stephen Dooley ensured Derry maintained their unbeaten run during pre-season, winning 4-2 in Chris Morrow’s testimonial game last night.
Unfortunately Shane McEleney headed one past his own goalkeeper Gerard Doherty, while Stephen O’Flynn also scored against his old club from the penalty spot.