The Parramatta back-rower will have surgery on his damaged knee on Friday, joining the club’s growing unavailable list.
Watmough’s season-ending injury comes on top of the feud between enigmatic halfback Chris Sandow and the club.
Parramatta were thrashed by Canterbury last Friday and are at long odds to make the top eight.
Watmough wrote: “Shattered to miss the rest of the year with injury... It's the first time in 14yrs of first grade that I will finish the year injured.
“My first major injury, not a bad run...will have surgery on Friday.
“Thanks everyone for the support especially all my @theparraeels team mates and staff... it's been a tough year u have patched me together to get me to each game but it finally gave out.
“Also a big thanks to all to my friends,fans and all my family for the support this year even if u didn't support parra u still supported me and it will never be forgotten.
“U guys know who u are ... We will be back next year ready to go...”
