Petrie severed a tendon during Glasgow's 37-9 defeat by Edinburgh which, if not operated on, could have resulted in him losing use of it permanently. The 26-year-old, who has been in fine form for the Warriors this season despite their poor form, will be out of action for up to two months.
He said: "It's frustrating because it seemed such an innocuous injury. "There is only one tendon in your thumb and if it is torn or severed, it can't work. They will have to open up the whole thumb to locate the problem."
Petrie has now set his sights on forcing his way into the squad for the Rugby World Cup in Australia in November. Uncapped Warriors team-mate Andrew Wilson has been called up to replace Petrie at the Scotland training session at Murrayfield.