Gallen was the first forced from the field after injuring his knee in an awkward tackle.
Early reports suggest Gallen might have suffered a medial ligament strain which could see him sidelined anywhere from 2-10 weeks.
Fifita, on the other hand, could be facing a longer stint on the sidelines with fears he might have suffered an ACL injury.
Very innocuous injury mechanism here for Andrew Fifita and his left knee injury. Hope I am wrong here but slight concern for ACL injury as he changed direction prior to contact. Hope that’s not the case #NRLDragonsSharks pic.twitter.com/s1XV2sTWlT
— NRL PHYSIO (@nrlphysio) April 13, 2018
An ACL injury would see Fifita miss the rest of the season.
Graham appeared to have a hamstring injury, while Lewis reportedly suffered a cork to his leg.
All four players will be sent for scans to ascertain the extent of the injuries.