Hampshire batsman Aneurin Donald has suffered a setback in his recovery from anterior cruciate ligament surgery.
Welshman Donald, 24, missed the entire 2020 season after a knee operation in December 2019 to repair a tear.
The right-handed former Glamorgan and England Under-19 player was set to return for the start of this season.
"It's something we're monitoring in the coming days," director of cricket Giles White told BBC Radio Solent. "But he's a question mark for the season start."
He added: "We're not quite sure of the exact extent, but over the next of couple of days it should become a lot clearer."
Donald signed a two-year contract extension with Hampshire in February 2020 despite having to sit out all of last season.
There is better news for Hampshire, however, with England all-rounder Liam Dawson looking set for a return after a ruptured Achilles tendon in August ended his 2020 season prematurely.
He is set to play in a two-day friendly against Sussex from Thursday after a winter's worth of rehabilitation, White confirmed.
Left-arm seamer Keith Barker is also doubtful for Hampshire's County Championship opening round against Leicestershire from 8 April with a hamstring problem.