Mellor, who injured his knee in December against Warrington, is expected to be out for the first four to five games of the competition.
Prop Eamon O’Carroll has undergone an operation on his shoulder. Widnes coach Denis Betts said O’Carroll will be sidelined for three months.
Outside back Dean will also be out for 12 weeks, according to Betts.
The Vikings open their 2017 Super League campaign on February 10 at home against Huddersfield.