England batsman Alex Hales missed Nottinghamshire's One-Day Cup game against Lancashire on Friday because of "personal reasons".
The Notts website said: "Alex Hales has made himself unavailable for selection for personal reasons and no timetable has been set for his return to action."
The 30-year-old is due to join up with the England squad for their World Cup preparations at the end of the month.
England have made no comment on his absence.
No other explanation for Hales' omission from the Notts side has been offered.
Without him, the home side piled on 417-7 at Trent Bridge, with Joe Clarke making 139 from 99 deliveries.
Lancashire fell just short of the second-highest chase in List A history, closing on 406-9 to lose by 11 runs.