Andrea Orlandi and Will Hoskins' hopes of helping Albion during the run-in have suffered a fresh setback.
They have become the latest victims of the virus which has bugged the Albion camp.
Orlandi has still not fully recovered from a thigh injury which has ruled the Spaniard out of midfield contention for the last five matches.
The comeback plans of striker Hoskins after more than a year out with serious knee damage have been held up slightly by a minor calf injury.
The Seagulls should have Leo Ulloa, Dale Stephens and Inigo Calderon all back from the virus for Middlesbrough's visit tomorrow.
The trio missed Tuesday's 1-0 defeat at Sheffield Wednesday.
Matt Upson was an earlier victim of the bug which has also affected members of staff.