The former Norwich City player came off in the 39th minute of Saturday's League Two home game with Southend United after feeling discomfort in his hamstring and he will now be sidelined for the remainder of the campaign.
Power, a former Republic of Ireland under-21 international, 22, joined the club in January on a permanent basis from the Canaries.
He had previously spent loan spells at Dutch club Dordrecht, Ross County and Kings Lynn Town.
The winger has made 13 appearances for Harrogate, finding the net in the 3-1 victory at Crawley in early February.
Power's injury absence is the second blow to befall Simon Weaver's side this month.
Loan player Josh March was ruled out for the remainder of the season after sustaining a knee injury in the 3-0 victory over Colchester United on March 9.
The striker returned to parent club Forest Green following the injury after scoring five times in an encouraging ten-match spell at Harrogate.