Aberdeen captain Russell Anderson will be missing for between four and six weeks after having a knee operation.
The need for surgery was hastened by an injury sustained during last week's Premiership defeat at St Johnstone.
Prior to that the 35-year-old centre-back had played in three of the Dons' matches in Europa League qualifying.
He is likely to miss the league matches away to Celtic and Dundee and at home to Ross County and Inverness CT, plus the League cup tie against Livingston.
With the break for international football falling in the second week of October, a realistic target for Anderson could be the Premiership match at Hamilton on 18 October.
Anderson spent more than a decade at Pittodrie before a £1m move to Sunderland in 2007 followed by loans to Plymouth and Burnley and time at Derby.
He returned to Aberdeen at the beginning of 2012 and signed a with Derek McInnes's side in May to take him to the end of the current campaign.