Mattock has a foot injury, Smallwood is struggling with a hamstring problem while Frecklington suffered a dead leg in midweek and all three are doubtful.
Boss Steve Evans has a decision to make about his goalkeeper, with Adam Collin tipped to keep his place in front of Kelle Roos following an impressive showing in his first appearance since March in midweek.
Farrend Rawson (groin) is still not quite ready while Kirk Broadfoot has four games left of his suspension as the Millers chase their first three-pointer of the campaign.
Fulham will check on recent signing Sakari Matilla and defender Shaun Hutchinson.
Both players sustained knocks last Saturday and missed the Capital One Cup win against Sheffield United in midweek.
Jamie O’Hara was given the evening off as the Cottagers progressed to round three but the midfielder is expected to be back in the squad for the trip to South Yorkshire.
Fulham this week signed Cardiff goalkeeper Joe Lewis on loan until the end of the season and, after providing back-up on the bench on Tuesday night, he will be among the substitutes once more.