Scott Brown is to seek specialist advice on his ongoing ankle problem, with the Celtic skipper set to be sidelined for longer than anticipated.
The midfielder was expected to be back in contention for the Hoops' Scottish Premier League clash with Hearts on Sunday.
Following a number of weeks out of action, Neil Lennon was keen to bring the Scotland international back into his plans.
He has, however, been unable to shake off the injury.
Brown first damaged his ankle during an international run-out against Denmark in 2009 and aggravated the problem during Celtic's recent 4-2 defeat to Old Firm rivals Rangers.
The problem has required two operations and continues to hamper the 26-year-old's progress.
Lennon is determined to get to the bottom of the issue and has confirmed that Brown is to be sent for further medical tests.
He said: "He's going to see a specialist in the next few days. He will be out on Sunday too.
"I don't think it will require surgery but it might just be that it will take a bit longer than we first thought.
"We're hoping it's not as severe as a few months, but it might be a bit longer than a couple of weeks."