Neil Lennon has fired back in his war of words with Leigh Griffiths as he claimed the Celtic striker snubbed the offer of lockdown training sessions.
The former Hoops boss was left furious last summer when the Scotland frontman turned up for pre-season out of shape.
Things did not improve over the following campaign and the 30-year-old spent much of the season on the bench.
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Out-of-contract Griffiths - who is still waiting to learn if new Celtic manager Ange Postecoglou will offer him a new deal - fired back earlier this week, claiming he was "at times" given a raw deal by Lennon and then caretaker boss John Kennedy following the Northern Irishman's February exit.
But those words drew a blunt rebuke from his former boss as Lennon said Griffiths failed to join his team-mates in taking up the chance to put in extra sessions during last year's Covid-19 shutdown.
Lennon issued a further warning to the hitman, telling Griffiths his days at the top are numbered if he does not buck up his ideas.
"He let himself down," he told BBC Scotland's Euros Breakfast Show. "He's on full pay for the three months of lockdown and he comes back, totally out of condition and a stone overweight, when he couldn't afford to be because he hadn't played much football in the previous 18 months to two years.
"We had worked really hard with him to get him back on track and before lockdown, he was in the team and scoring goals and doing absolutely fine.
"Then he comes back completely out of condition, way, way behind any of the rest of them and for me, that was totally unacceptable.
"During the lockdown, the three months off, we opened the training ground. You couldn't come into the building but my fitness coach set up fitness training for the players every day.
"So you would come in, in groups of two, and train for an hour a day - fitness work, every day.
"Callum McGregor, Scott Brown, James Forrest, Greg Taylor, Jonny Hayes - all the lads that lived in Scotland came in. Leigh didn't come in one day, not one day during the lockdown. You can take a horse to water but you can't force it to drink.
"He's saying, 'I'll prove people wrong' - he hasn't proved anybody wrong. He's not at the level of being a Champions League player, he didn't get picked for Scotland - you have to ask why.
"He'll say he didn't play enough games, towards the end of the season I wasn't there, John (Kennedy) obviously felt that he wasn't in the right frame of mind or condition to play for Celtic, which is a very high standard and I don't think Leigh got anywhere near those standards over the last year or so."