The reigning man of steel had to be stretchered from the field after he was injured in the act of scoring a try in Saints’ 40-10 win.
"He's had an X-ray and has been cleared of any fracture, which is good news," said Saints coach Daniel Anderson.
"He's currently undertaking an MRI scan to determine what ligament or soft tissue damage has occurred."
Anderson added: "I'd name Paul in the team but the doctors are likely to rule him out later in the week."
Saints will also be without captain Paul Sculthorpe, who is still recovering from knee surgery, and loose-forward Jason Hooper may miss the game with a shoulder injury sustained in during pre-season training in Dubai.
It is not known whether Wellens will be fit in time for the Carnegie World Club Challenge against Brisbane Broncos in three weeks’ time.