Alistair Johnston is reportedly set to miss the start of the season through injury.
It's claimed the right-back, 24, has yet to return to Celtic training in pre-season.
Johnston enjoyed a stunning start to life at Parkhead before an ankle injury in the Scottish Cup semi-final against Rangers.
The defender was sidelined but returned for the showpiece final against Inverness at Hampden.
However, The Scottish Sun claim Johnston has not returned to Celtic training since the end of the season.
A report states Johnston could miss opening matches of the new Scottish Premiership season in a huge blow to Brendan Rodgers.
Canada international Johnston had played for his country in June but was left out of the Gold Cup squad with manager John Herdman admitting he was still feeling the effects of the ankle injury.
Speaking last month, Herdman commented: "Some players need a break to recover from injury.
"Alistair Johnston was carrying an injury he picked up on club duty with Celtic.
"So we've got some young lads that we'll start looking at for this Gold Cup.
"I would have loved to have the same squad as for the Nations League, but it won't happen."
Fellow Parkhead defender Cameron Carter-Vickers, meanwhile, is pushing to return for the first league clash against Ross County.
The centre-back missed the end of last season through a knee injury.
And after surgery a return in late August had been expected. But reports earlier this week suggested Carter-Vickers has progressed well in his injury rehab and joined his team-mates in Portugal for pre-season.
It's thought the US international will take part in light training in Portugal ahead of a hoped return for the league curtain-raiaser on August 5 at Celtic Park.
