Celtic hero Martin O'Neill feels midfielder David Turnbull "does not function as strongly" as he should in some games.
The Scotland international has scored seven goals for this season but has not been a regular starter over the last two campaigns.
And O'Neill feels the 24-year-old needs to do more when he is given a chance.
Speaking to PLZ Soccer, he said: "Turnbull, sometimes you feel he can turn up in a game and really dominate it.
"And other times, he doesn’t function as strongly as you think he should do in games."
Meanwhile, Celtic have released a statement confirming their stance on the recent European Super League court ruling, ruling out any involvement in the competition.
It comes after the rebel clubs involved won their case at the Court of Justice on Thursday.
And the Scottish champions have reaffirmed their desire to stay within the UEFA framework.
A club statement read: "Celtic Football Club has noted today's judgement delivered by the European Court of Justice.
"The resolution regarding the framework for prior authorization of other competitions refers to outdated UEFA statutes that were already amended in June 2022.
"We must be clear that this does not in any way endorse or approve the so-called 'Super League' project.
"Celtic plays an important, leading role within the European Club Association framework and as a club, we are fully committed to working through the ECA, alongside our fellow European clubs to uphold the values that define European football.
"We can only achieve our objectives through the strong partnership ECA enjoys with UEFA.
"The wider European football community is not supportive of the ESL, and Celtic, like many other clubs, will continue to promote the interests and protection of football’s broader family through the ECA and UEFA."
