The centre suffered an ankle injury during his try-scoring cameo against Newport Gwent Dragons on New Year's Eve.
And following further investigation it has been discovered that the 22-year-old has suffered significant ligament damage.
He will subsequently miss the Ospreys crucial Heineken Cup matches with Leicester Tigers and Benetton Treviso and at least the first three fixtures of the RBS 6 Nations, against Ireland, France and Italy.
"Ashley suffered a significant ligament injury to his ankle during the New Year's Eve fixture at Rodney Parade," said Ospreys head of physio.
"We've conducted investigations over the course of the last week to determine the full extent of the ligament damage and plan his rehabilitation effectively.
"Based on the advice received, we are currently treating this as a 6-8 week injury so would expect to see him back in action by the end of February."
Jamie Roberts and Jon Davies remain the tried and tested combination in the Welsh midfield, while the likes of Scott Williams and James Hook offer further options.