Marvin Sordell is rated as 50/50 for Watford's home clash against Bristol City.
The striker, Watford's leading scorer this season with five goals, turned his ankle 37 minutes into Saturday's goalless draw at Doncaster and was subsequently forced off.
He is now facing a race against time to be fit to face the resurgent Robins, who have taken 13 points from the last 15 under Derek McInnes and saw off leaders Southampton 2-0 at the weekend.
Craig Beattie came on to replace Sordell at the Keepmoat Stadium and the on-loan Swansea forward will challenge Troy Deeney for what would be his first start for the club should manager Sean Dyche be forced into a change.
In-form midfielder Jonathan Hogg returns into contention having served a one-match ban and hands Dyche a selection poser with club captain John Eustace making his comeback from injury to take his place against Doncaster.
Defender Lloyd Doyley (thigh) continues to make progress but Tuesday may come too soon, while centre-back Martin Taylor (dislocated collarbone) and midfielder Stephen McGinn (knee) remain sidelined.
Derek McInnes has no new injury or suspension worries as he takes his in-form side to Hertfordshire.
Defenders Louis Carey and Jamie McAllister are fit again following their respective knee and ankle injuries and are available to McInnes for the trip to the Hornets.
However, the City manager is unlikely to change his starting XI from the side which beat table-topping Southampton 2-0 at Ashton Gate on Saturday.
Striker Jon Stead has resumed full training after a slight groin problem but is not likely to be involved on Tuesday, with the club targeting the weekend clash with Middlesbrough for his potential return to the matchday squad.
Fringe players Ryan Taylor (broken metatarsal) and Nicky Hunt (knee) remain sidelined.
