The 23-year-old had scans on Monday which revealed an injury to the ligaments that run between the fibula and tibia in the front of his right ankle, known as syndesmosis.
Swans coach John Longmire confirmed that the talented midfielder could miss up to a month with the injury.
“He’s a got a slight syndesmosis injury in his ankle, which means he’ll probably miss about four weeks,” Longmire told sydneyswans.com.au.
“It could be either side of that though, so it could be a shorter time frame than that, or at worst it could be a little bit longer.
“We’re expecting about four weeks at the present time, but it will take a good week or so before we get a good idea of how it is.”
While the injury will not require surgery, Longmire said Hannebery’s ligaments would need to fully heal before he could return to the field.
“It doesn’t require an operation; it’s more a time thing,” he said.
“He’ll be non-weight bearing for the next ten days and hopefully it’s okay after that and we’ll have more idea after that.
“We have to wait and see, but at the moment it’s four weeks.”
Longmire admitted that Hannebery would be a big loss for the Swans, who travel to Melbourne to take on Richmond at the MCG on Friday night.
“He’s been a really good player for us,” he said.
“Probably since the first month when he was a bit quiet, he’s really had a really solid season.
“He’s back to playing where he was last year.
“He was a little bit quiet on the weekend, but prior to that he’s been one of our better running players and one of our best midfielders.”
With Hannebery out of the side and Ben McGlynn (fractured thumb) and Tom Mitchell (ankle) also unavailable for selection this week, Longmire said the Swans would look to their up-and-coming midfielders to take on more responsibility in their absence.
The coach said he had been pleased with the efforts of Harry Cunningham and Jake Lloyd in recent weeks, and had full confidence in their ability to step up this week against the Tigers.
“(Hannebery’s) got a good combination of inside and outside game, which is so important, but he’s unfortunately out,” Longmire said.
“We’ve been fortunate that we’ve been blooding some extra midfielders through that area like Harry Cunningham and Jack Lloyd and players like that who have been playing pretty well for us week in, week out, so now they just get more responsibility.”
Longmire said he’d also been impressed with a number of players for the Swans reserves over the last few weeks, and would make a decision on Hannebery’s replacement in the next two days.
“We’ll just sit down in the next 24-48 hours and work out who the replacements are,” he said.
“We’ve had a couple of players playing pretty well in the reserves, so we’ll work through that in the next 48 hours.
“We’re confident we’ve got the players who can come in and fill those roles.”