Celtic trio Kieran Tierney, Kasper Hogh and Callum Osmand all missed training on Tuesday ahead of the Scottish Premiership match against Aberdeen.
Martin O'Neill's side host the Pittodrie club at Celtic Park on Wednesday evening.
However, there are now question marks over the availability of Tierney, Hogh and Osmand after they were not involved in training at Lennoxtown, according to Sky Sports.
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Hogh didn't make the matchday squad for the win over Falkirk last weekend, Tierney was forced off and Osmand leaving the stadium wearing a protective boot.
However, Celtic captain Callum McGregor provided a boost as he returned to training.
The midfielder missed the weekend's match due to illness but appears to be back in contention for the visit of Aberdeen in midweek.
