The Hornets suffered their fourth consecutive defeat at the hands of rock-bottom Peterborough on Saturday but with no injuries or suspensions, Mackay could keep faith with the same players.
Winger Will Buckley was overlooked for a place on the bench against Posh, despite a midweek run-out for the reserves following a thigh injury, but he could come into contention for a first appearance since his January move from Rochdale.
Tom Cleverley made his return from a ban against Posh in place of Jon Harley and the on-loan Manchester United midfielder should retain his place.
If Mackay is thinking of shuffling his pack around, striker Will Hoskins will be hoping to be a beneficiary after he replaced Danny Graham midway through the second half on Saturday.
The game against Town is one they can ill-afford to lose as their poor run of form has seen an alarming side down the table and the Hornets are now just point above the drop zone.