Dunn, 32, starred in the opening half-hour of Wednesday night's 1-0 victory over Sheffield Wednesday, setting-up up Grant Hanley's winner at the end of a fine solo run.
But his evening was cut short after the half hour and Rovers' medical staff are waiting on the results of a scan on a calf injury sustained by the playmaker.
Spanish forward Ruben Rochina could push for his first start since September's 2-1 win over Barnsley having replaced Dunn in midweek, although caretaker manager Eric Black may turn to Danny Murphy having left the club captain on the bench for the previous two matches.
Markus Olsson has returned to training following his hamstring problem but is not yet ready for first-team action.
Montenegro's Simon Vukcevic (groin) and Portugal Under-21 winger Fabio Nunes (hamstring) are set to remain on the sidelines for six to 10 days and three to four weeks respectively following injuries sustained on international duty.
Watford's Daniel Pudil and Nathaniel Chalobah will miss the trip through suspension.
Both were given their marching orders during Tuesday's clash at Cardiff, meaning the Hornets were forced to play the final 18 minutes with just nine men as the hosts went on to grab an injury-time winner to triumph 2-1.
Some good news for Watford though is that left-back Pudil's three-match ban has been reduced to one game, after Cardiff supported an appeal.
Elsewhere, skipper John Eustace (back), Piccoli Neuton (ankle), Nyron Nosworthy and Prince Buaben (both hamstring) continue to miss out.
But there is better news regarding Geoffrey Mujangi Bia and Joel Ekstrand, with the pair back in training following groin and ankle injuries.
However, it remains to be seen whether either will be involved at Ewood Park.