Centre-back Dael Fry and midfielder Marcus Tavernier have both been ruled out for the next few weeks with calf and hamstring injuries respectively.
Defender Anfernee Dijksteel will also miss the match and the rest of the season after undergoing an operation on an ankle issue which he picked up at Swansea.
Boro’s 3-1 defeat at Bournemouth last time out left them seven points adrift of the Championship play-off places with seven games to go.
Watford, meanwhile, will be looking to bolster their automatic promotion hopes and are second in the table after six consecutive wins.
Boro were beaten 1-0 when the two sides met at Vicarage Road on the opening day of the season.
Here’s who we think could start for Boro against the Hornets.
. GK: Marcus Bettinelli
Has started every league game for Boro this season but has had a mixed campaign. Photo: Alex Burstow
1. GK: Marcus Bettinelli
Has started every league game for Boro this season but has had a mixed campaign. Photo: Alex Burstow
2. RB: Darnell Fisher
Endured a tough game at Bournemouth but has performed well since signing from Preston. Photo: Catherine Ivill
3. CB: Grant Hall
Has been a key player at the back since returning from injury. Dael Fry's injury only increases Hall's importance. Photo: Stu Forster
4. CB: Paddy McNair
Played at Bournemouth after representing Northern Ireland during the international break. Fry's injury means he'll have to start at the back. Photo: Alex Pantling