Preston midfielder Ben Pringle, who used to play for the Millers, and Celtic counterpart Kundai Benyu have both joined the League One club on loan for the remainder of the season and will hope to feature for the first time.
However, there have been departures too with midfielder Paul Green having left on loan to League Two Crewe and striker Darius Osei having had his contract cancelled.
Wellens will watch from the stands as he serves a one-match touchline ban handed out by the Football Association as a result of comments made to match officials after the 1-0 defeat at Shrewsbury on January 1.
Rotherham could hand new signing Michael Smith a debut.
Smith joined the Millers from Bury for an undisclosed fee on Thursday and might make a first start.
But Lee Frecklington will not feature after the skipper’s five-year stay at the club came to an end when he joined Lincoln.
Darren Potter (Achilles) is out until at least next month but Jon Taylor could play after a two-month absence due to a knee injury.
Watford boss Javi Gracia does not think Abdoulaye Doucoure's form will be affected by his omission from France's latest squad.