Long made his tally seven goals in the last six games last weekend with the winner in the FA Cup defeat of West Brom, but was replaced after taking a knock.
However, the Republic of Ireland international is fit to keep his place in attack.
The Royals should also have Andy Griffin available for selection.
The right-back was rested for the FA Cup win and saw Shaun Cummings turn in an excellent performance in his place to give manager Brian McDermott a dilemma.
Defender Zurab Khizanishvili is a doubt after he picked up a knee injury, but club captain Ivar Ingimarsson is available after shaking off a long-term hamstring injury which has so far ruled him out of the whole season.