However, the blow has been softened by the confirmation that tight-head Adam is lined up for a return to action next weekend after recovering from surgery to repair the shoulder he damaged on British & Irish Lions duty in the summer, slightly ahead of schedule.
"In Duncan's case, the medical advice is to keep him off the injured foot for six weeks to allow the bone heal," said Ospreys physio Chris Towers.
"Once it is confirmed that the bone has healed, we will then move him onto a progressive return to playing.
"Adam returned to full training at the end of last week, including contact, without any reaction, which is obviously excellent news.
"We are now looking to involve him in a normal rugby programme in training, which will see him available for selection against Viadana at the Liberty Stadium on Saturday."
Meanwhile Barry Davies has been ruled out of action for a period of two to four weeks after undergoing keyhole surgery to repair a groin injury.
The 28 year old full-back, who has been in eye-catching form since the Ospreys brought him back to Welsh rugby from Brive during the summer, had the operation on Friday and now faces a spell on the sidelines.
"Barry has failed to recover from a groin problem which has prevented him from training fully in recent weeks, so a decision was made in his best interests to opt for surgery," added Towers.
"It was not a major procedure, and with an aggressive rehab programme over the next couple of weeks, he is only likely to be unavailable for selection for a period of two to four weeks."
63x46.png){kind=logo}