The 24-year-old former Leeds and London Broncos player rejoined Rovers on a short-term deal in May and was set to make his playing return when his 16-month ban for cocaine use expires after July 14.
However, he has now been ruled out for the next three months and must now hope to have impressed enough in training to be offered a new deal for next season.
Hull KR physio Trent Bowden told the club’s website: “Thomas suffered an injury on his foot in training which required surgery. He’s likely to be out for three months.
“Thomas has been training quite well upon his return to the team and the injury is really unfortunate timing for him.”
Minns revealed on social media that the injury prevented him carrying the coffin of his grandfather at his funeral which left him heartbroken but he sent out a defiant message.
“I’ve got so much to offer,” he said. “I will keep a positive attitude and keep moving in the right direction until I get where I need to be.”