Mansour sustained the injury when he collided with Anthony Don’s knee on Sunday, immediately exiting the game in pain.
The 27-year old was expected to miss up to 12 weeks after requiring surgery, which was already a massive blow to the Panthers.
Alexander, who is a halves consultant for Penrith, has revealed that Mansour may not play again this season.
“It was a nasty fracture, it was more than a fracture,” Alexander told Fox Sports.
“It’s done a lot of damage, there’s bone fragments in there, it’s not just a depressed fracture, it’s a lot more than that.
“Norm Southern, who has been our club doctor (since 1979) … he said it’s the worst cheekbone injury he’s seen.
“Best case scenario for Josh is three months. Worst case scenario is he’ll need a bone graft and that could be his season.
“We’re hoping when he goes in there the doctors can put it back together and he might be on the field within 12 weeks.”
Mansour has had a poor run of late, injuring his knee at the end of 2016 which caused him to miss half the 2017 season.
He is set to be replaced by Dallin Watene-Zelezniak for Sunday’s game against Cronulla.
The Panthers sit second on the NRL ladder with five wins and one loss.