A day after it was announced Sam Reid would be sidelined for at least six weeks with another tear in his left quad, and there is also doubt over Roberts-Thomson playing again for the Swans in 2013.
The popular utility first injured his knee against Geelong in round four, requiring surgery.
It was then discovered there was more floating cartilage in the knee than initially thought, with the club's medical staff admitting his recovery time was unpredictable.
Still unable to run, the odds of the two-time Premiership winner returning this year are lengthening, although coach John Longmire hasn't given up hope.
"He's been very slow," Longmire said.
"We thought he'd be back after the bye, but he's got some bone bruising in his knee and it's just taking a long time to heal.
"He's not running, so he's a fair way off senior footy.
"I'm not writing him off yet, we're still hopeful that he'll get back, but he needs everything going right from now on in."
There is some good news on the Swans' injury front, with Gary Rohan set to return to action with the reserves on Sunday.
Longmire also hopes Rhyce Shaw (abdominal) and Lewis Jetta (shin) will train this week, but Rohan is looming as one of the good news stories of the season for the Swans.
Sidelined since his terrible leg break in round four last year, Rohan has two more training sessions to get through before he will get the green light for a limited return in the reserves.
"If he trains ok and pulls up ok, he'll play in our reserves," Longmire said.
"It might only be for 30 minutes, but if he pulls up ok he'll play.
"He's a very popular player, so to have him out on thetraining track has been fantastic, and it'll be even better to see him play."
There is still no timeframe or consideration, however, for Rohan's potential return to senior football.
Longmire also expects Shaw to train both sessions this week, although he admits he's "not too keen on him playing just yet".
Jetta, meanwhile, was having another scan this week on his injured shin, which has kept him out for the past five weeks.
Similar to Shaw, at first the club hoped it would only be a two-week injury, but the Swans are taking a very cautious approach with the 24-year-old.
"'Gibbsy' (club doctor Nathan Gibbs) described it as bone bruising," Longmire said.
"You have to be careful that you don't keep training and running and playing on it because it can turn into a more serious injury."
Asked if a fracture or shin splints was the concern, Longmire said, "If he'd kept on playing, that's where it could've headed."
With Adam Goodes recovering from knee surgery and Mitch Morton battling a quad, added to Alex Johnson (knee) and Marty Mattner (retirement), the Swans are facing their biggest injury crisis in some time.
But Longmire is doing his best to take the situation in his stride.
"We've been fortunate the last couple of years, and particularly last year, to have a good run," he said.
"This year we're not having the same run obviously, but so are Collingwood and Fremantle have had a few challenges.
"Whilst it would've been great to have Goodes and Jetta and Shaw and LRT and Alex Johnson available, we have been able to unearth some kids who have been pretty good.
"We saw another on the weekend with Brandon Jack.
"We've been able to use a number of players this year and bring the kids in and, to their credit, they've performed quite well."
