Dolly the Sheep is five and a half years old
Professor Ian Wilmut, a member of the team at the Roslin Institute in Edinburgh, said the condition may have arisen because of genetic defects caused by the cloning process.
Professor Wilmut has called for a research programme to establish the impact cloning has on animal health.
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Mr Wilmut said: "There is no way of knowing if this is down to cloning or whether it is a coincidence.
"We will never know the answer to that question."
He later told BBC Radio 4's Today programme that there needed to be a systematic assessment of the health of cloned animals.
And he accepted that scientists may be too commercially motivated.
But he continued: "This is a very young technique.
"It has great potential. As well as studying the animals that are there already we have to continue with the process to improve and use the technology."
Survival struggle
But Dan Lyons, of the animal protection group CAGE, told the programme that this process could never be perfected.
"Biology is not like Lego, it's not like Meccano, you can't just interfere with one aspect of an animal's system and expect the rest of the system to continue to function perfectly."
The animal welfare group Compassion in World Farming has also called for a halt to cloning.
Its director, Joyce D'Silva, told BBC Radio 5 Live: "I think of the hundreds and hundreds of other cloned lambs who have been born and had malformed hearts, lungs or kidneys.
"They have struggled to survive for a few days and then had their lungs filled with fluid and gasped their way to death or had to be put our of their misery by their creators.
"That is the real story of cloning."
It is unusual but not unknown for a five and a half year old sheep to develop arthritis.
This has raised the question of whether the cloning process led to Dolly's problem and whether cloning always gives rise to unhealthy animals.
Many cloning companies have reported that their animals are healthy.
But there has been no independent assessment of the long term health of cloned animals.
And there is anecdotal evidence of animals being born overweight, malformed and with damaged immune systems.