Celtic captain Scott Brown is expected to miss the start of the Scottish Premiership season and could be out for a total of three months with a serious hamstring injury.
The midfielder was stretchered off in the early stages of Celtic's 1-1 friendly draw with Rapid Vienna on Sunday.
New Bhoys manager Ronny Deila was initially optimistic over the diagnosis, but BBC Sport learned on Tuesday that scans indicated that the 29-year-old faces a layoff of up to eight weeks.
Brown will therefore be unavailable for the preliminary rounds of the Champions League, in which Celtic firstly take on Icelandic side KR Reykjavik on July 15, and Scotland's opening Euro 2016 qualifier against World Cup finalists Germany on September 7.
The Scottish champions begin the defence of their domestic title at St Johnstone on August 13.
