Harrad signed from Burton Albion on Thursday but sat out the win over Oxford on Saturday after a jaw operation.
Sampson said: "Shaun had a long-standing operation on his jaw scheduled in for Friday but he will train with us for the first time on Tuesday.
"Even if he had still been at Burton he wouldn't have been available.
"He's here for two-and-a-half years so to miss one game isn't too bad."
Source: PA
Source: PA