The out-of-form Bulldogs are hoping the mumps virus they suspect has struck down three star players will not spread throughout the NRL premiers' squad.

Internationals Sonny Bill Williams and Willie Tonga underwent blood tests to confirm whether they have contracted the mumps.

The pair would have picked up the viral infection from utility Reni Maitua and Bulldogs football manager Brad Clyde.

The timing couldn't be worse for the premiers, who have lost their past three matches after thrashing St George Illawarra in the opening round.

Maitua reportedly lost 7kg and spent two weeks in severe pain after contracting mumps, a viral infection spread by infected saliva that can cause weakness and fatigue.

"By the next morning I couldn't move my hands at all," Maitua told Channel Nine.

"It travelled to my shoulders the next day and then my knees the day after that.

"It put me on my back for another five or six days."

Maitua said he rang Williams to check on his condition but the New Zealand international "hung up on me".

"Unfortunately Sonny Bill and Willie Tonga have come down with it this morning," said Maitua, who has been sidelined with an ankle injury this year.

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