Hull FC forwards Kane Evans and Manu Ma’u will miss the start of the new Super League season.
Mau is likely to miss at least the first month of the season with a hamstring injury, while Evans has injured his pectoral muscle.
Evans was banned for the first three games of the season anyway, but seems likely to spend further time on the sidelines.
The Airlie Birds are already without long-term absentee Scott Taylor.
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Coach Brett Hodgson told the club’s official website: “It is obviously very disappointing news for the players and the club as they were both training exceptionally well.
“Unfortunately, there is always a risk of injury in pre-season. The Kane one is particularly unfortunate as it came from a contact during the training game against London.
“Alongside Scott, they are three notable absentees for us. But they will all have a significant role to play in our season.
“We’ve got a handful of others with minor niggles who we may choose to rest up this weekend rather than play in the Leeds friendly.”
“I am not willing to risk anyone who isn’t 100% as it is a long season ahead and we’ll need all our players to contribute at some stage.
“Whilst its obviously disappointing for those individuals, it also presents a great opportunity for players in our squad to step up to the plate and take their chance.”
Hodgson has at least had more positive news over prop Chris Satae (calf) and Josh Bowden (quad). Both are expected to be in contention for the season opener against Wakefield.
Jamie Shaul (ankle), Josh Reynolds (knee) and Connor Wynne (knee) are also due to be back in full training next week.
Loose forward Joe Cator is making progress following a ruptured Achilles and the club say he could be available in the early rounds.