Jedinak suffered a broken nose and cheekbone after being caught by a stray arm against Huddersfield last week, forcing him to miss Saturday's 2-1 win over Charlton.
Palace hope the Australia international will soon be able to play in a face mask but are not expected to risk him at Vicarage Road.
However, fellow midfielder Kagisho Dikgacoi could return to the squad after South Africa's exit from the African Nations Cup.
Andre Moritz needs a check on an ankle injury while Alex Nimely (hamstring), Paddy McCarthy, Joel Ward (both groin) and Owen Garvan (knee) are still out.
Veteran striker Kevin Phillips could feature against his old club after making his debut against Charlton.
Hosts Watford will run the rule over defenders Joel Ekstrand and Nyron Nosworthy. Ekstrand was forced off late on in last weekend's 2-1 win over Bolton nursing a knee injury and remains a doubt, with a decision due to be made as late as possible.
Nosworthy replaced Ekstrand for the closing stages but he has been on international duty with Jamaica this week and the lengthy travelling may have taken its toll ahead of his late return to Hertfordshire.
Boss Gianfranco Zola could have a ready-made replacement at hand in the shape of Tommie Hoban, who stepped up his fitness after an Achilles injury by representing the Republic of Ireland Under-19s in midweek.
Midfielder Ikechi Anya (hamstring) and defender Neuton (back) remain out.