Donald, 24, joined Hampshire from Glamorgan in August 2018 citing his desire to play international cricket and had a strong first full season with the club, scoring 554 County Championship runs at 39.57 and making 203 T20 Blast runs while striking at 138.09.
But he suffered an ACL injury in December 2019 which required surgery, ruling him out for the whole of the 2020 summer, and reported a knee twist during an intra-squad match in March which has required further reconstructive surgery.
The news is a significant blow to Donald's career. Aged 19, he equalled the record for the fastest double-hundred in first-class cricket by hitting 234 off 136 balls against Derbyshire at Colwyn Bay, and he had shown flashes of brilliance in white-ball cricket as a top-order batter. James Clegg, Hampshire's head of sports science and medicine, said that he was "absolutely confident" that Donald would be able to resume his career in 2022 despite another setback.
"Most ACL failures occur when a new unstable episode disrupts the repaired ligament graft," Clegg said. "In Aneurin's case, the scans showed that his repaired graft was slowly failing - ultimately you rely on the harvested graft tissue repairing and being able to withstand the demands cricket places on it.
"It is really unfortunate Aneurin finds himself back in an ACL rehabilitation programme and these are inevitably long, drawn-out processes but he is the model professional and continues to go above and beyond. Whilst he now unfortunately faces a significant spell on the sidelines, we are targeting a full return to play in 2022 and are absolutely confident Aneurin will return despite this setback."
"I'm devastated to be back on the sidelines following my reinjury," Donald said. "It's certainly a tough pill to swallow after such a long rehabilitation process that led to me being back in a position to feature on the pitch at the start of this pre-season.
"Unfortunately, after trying to continue without a functioning ACL, a scan showing a tear in my meniscus a few weeks later finally led to surgery being the only remaining option. Fortunately, with thanks to Andy Williams and his team at the Fortius Clinic, my second surgery was a success, and I have already begun to dive into the rehabilitation process once again with a full recovery fully expected."
Matt Roller is an assistant editor at ESPNcricinfo. @mroller98