كتب : وكالات
Both sides will be desperate to make up for a disappointing start to their Champions League group stage campaign when they meet at Ismailia Stadium on Sunday.
"It's a decisive and difficult game," Siasia, who was recently linked with Nigeria's vacant managerial seat, told FilGoal.com on Thursday.
"The outcome might see one team lose hope of going through and the other team regain it."
Heartland threw away their lead to draw 1-1 at home to six-time African Champions Ahli in their first game before slumping to a 1-0 defeat by Algeria's JS Kabylie.
Ismaili's start was worse as they lost 1-0 to Kabylie at home before suffering a heartbreaking 2-1 defeat by bitter rivals Ahli, who notched the winner in stoppage time.
"Our opponents are very good. They produced a fine performance against Ahli despite their loss," Siasia added.
"They will have the home advantage in Sunday's game and will have no option but to win to keep alive their hopes of reaching the next round. However, we will also eye nothing but a victory."
Kabylie top Group B with maximum six points, two ahead of Ahli. Heartland are third on one point while Ismaili lie at the bottom with no points.