The Canterbury Bulldogs have suffered a massive blow to their forward stocks as they attempt to keep their spot on top of the NRL ladder, as they face the Parramatta Eels in Round 14.

Already ruled out of this week's match due to a five-week suspension, the news for back-rower Sitili Tupouniua has gone from bad to worse.

According toย 9News' Danny Weidler, Tupouniua, who was set to return in Round 15, has injured his hamstring at training on Wednesday and is "expected to be out for an extended period".

The injury sees him join Jack Todd (arm) and Jaeman Salmon (ankle) on the sidelines for the foreseeable future.

Missing the entire pre-season due to injury, the forward has surprisingly only made six appearances this season, but has easily been one of the club's best players on the field when he enters the game off the interchange bench.

In six matches, he has scored three tries, made three line-breaks and 118 total tackles and averaged 102 running metres per game.