Hassell limped out of Saturday's defeat to Leicester with an ankle injury and is a major doubt for the visit to the Madejski Stadium.
"Bobby felt something pop in his Achilles in the first half. We will have to see how he is when things have settled down a little," Davey told the club's official website.
Striker Daniel Bogdanovic was unavailable at the weekend after returning to Malta for family reasons and could miss out once again.
Fellow frontman Andy Gray made his debut at Leicester after joining from Charlton but will be unavailable as he is cup-tied.
The match kicks off at 8pm.