Celtic midfielder Shunsuke Nakamura fears he could miss next week's Champions League group game against AC Milan due to injury.
The Japanese player damaged his left knee initially during Celtic's qualifying tie against Spartak Moscow and cannot strike a ball firmly without feeling a reaction.
He could now be forced out of the October 3 clash with reigning European champions Milan.
Nakamura, 29, told The Times: 'I have damaged the outer ligament of my left knee, and the Celtic team doctor told me it would be two to three weeks before I could get back to full fitness.
'If it proves possible I'd like to play in the Milan game, but we will see. It's only painful when I try to kick the ball with force.'
Celtic lost their opening group game to Shakhtar Donetsk last Tuesday and will be looking to win each of their three home matches to give themselves the best possible chance of reaching the last 16.
Losing Nakamura would hit their chances of upsetting the Italians, but the former Reggina playmaker admits it would not be wise to take any risks.
He added: 'I can get by, but when I think about the long season ahead, perhaps it would be better to get the problem sorted sooner rather than later. If not, I could aggravate it even more.'
Meanwhile, Celtic goalkeeper Artur Boruc is unlikely to face any punishment despite being photographed apparently making a rude hand gesture during Sunday's 3-2 defeat at Hibernian in the Clydesdale Bank Premier League.