Five-eighth Jarrod Mullen could miss up to four months of NRL action with a hamstring injury in a devastating blow to Newcastle’s premiership hopes.

On the same morning the Knights re-signed promising halfback Tyrone Roberts to a new two-year deal reports emerged that chief playmaker Mullen could miss the majority of the season.

Mullen sustained the injury in the Auckland Nines tournament and went to ground immediately, clutching the back of his leg.

News Limited is reporting the club is now fearing he has torn his hamstring off the bone and could be set for a long lay-off.

Fresh from being handed a new contract, it would seem 22-year-old Roberts is set for a major jump in responsibilities for at least the first half of the season.

Roberts played all 27 matches last season and is seen as a future leader at the Knights.

“Tyrone is an outstanding young man and has a wonderful future ahead of him,” said coach Wayne Bennett.

“It has been pleasing to see him grow in confidence and we are delighted he has re-signed with the club.

“Tyrone is one of our key young players who will be a long-term player at the Knights.”

Newcastle may consider moving Kurt Gidley from hooker to the halves to compensate for Mullen’s loss, but their other option is to give a start to former Canberra half Michael Dobson.

Gidley has been training to permanently take over from Danny Buderus at No.9, but is an experienced ball-player who could provide good support for Roberts.

Dobson will get his chance this weekend in a trial against Canberra in Tamworth, after being named in a 22-man Knights squad.

Mullen joins the list of serious injury worries to come out of the inaugural Nines, headed by an ACL injury to North Queensland’s Lachlan Coote.