Rizwan and Irfan both suffered hamstring injuries in the third match in Rawalpindi
The forward has been sidelined with a hamstring injury, last appearing in the 5-1 win over Lyon in the last 16 second leg clash on March 13, and has been waiting for medical clearance before he can feature.
Ernesto Valverde named 22 players on Monday who will travel to Manchester, with four to be left out of the 18-man matchday squad.
Dembele has impressed at Barcelona this season after struggling in his first campaign following a 147 million euro (126.77 million pounds) move from Borussia Dortmund in August 2017.