Former England batsman Gary Ballance is battling "anxiety and stress".
Ballance, who played 23 Tests and 16 ODIs between 2013 and 2017 has not played this season and has had health struggles recently.
The 30-year-old is working his way back to fitness and is also back in the nets but there is no time frame for his return to action.
A statement from Yorkshire read: "Gary is currently managing some heightened feelings of anxiety and stress following a long period of isolation due to the COVID-19 lockdown, his own recent viral illness and other personal factors.
"The post-viral symptoms have affected his physical preparation for this shortened cricket season. He is currently unavailable for selection and we are unable to put any timescales on his return to playing at this time.
"Gary's health and well-being remains our priority and the club and medical staff will continue to work closely with Gary to support his return to playing as soon as possible."
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