Winger McAnuff has a back injury and striker Ellington a knee problem and neither are likely to travel having missed Saturday's 1-1 draw with Blackpool.
Hornets fans may also have seen the last of Smith, with Reading expected to resurrect their £1.8million move for the striker.
Midfielder Don Cowie suffered no ill-effects following his return from a hamstring injury at the weekend and he will be involved once more.
Loan duo Henri Lansbury and Tom Cleverley have been given permission to play in the competition by parent clubs Arsenal and Manchester United.
