Seyfarth has enjoyed a mixed season, featuring in 17 of the Tigers' 22 games so far, though averaging just 40 metres and 38 minutes a game in the process. The injury is a double blow to their forward pack for this weekend's clash with the Dragons, having also lost James Tamou to a one-week suspension.
A pec tear usually sits between the 10-14 week recovery mark, meaning that while Seyfarth won't feature again in 2022, he will be fit to return to full training around mid-November.
The Wests Tigers have a desperate battle on their hands if they are to avoid the joint-venture's maiden wooden spoon this season, sitting on the same amount of competition points as the Gold Coast.
However, the drubbing at the hands of the Roosters means the Tigers are anchored to 16th, with a significantly worse for-and-against than the Titans, and clashes against the Dragons and Raiders to finish the year.
The Titans face the Knights this round while the Tigers take on the Red V at CommBank Stadium, with a win from either underdog having the potential to see them to dodge the bottom rung of the ladder.