Juncker was seen unsteady on his feet at a North Atlantic Treaty Organisation summit event - to the extent where the prime ministers of the Netherlands and Portugal had to prop him up - before having to be helped away in a wheelchair.
Juncker has previously revealed that he suffers from sciatica - a leg pain originating in the lower back - that can sometimes affect his movements.
Video footage of Juncker stumbling during a photo shoot at a North Atlantic Treaty Organisation summit on Wednesday had fueled speculation over his health, with some media outlets suggesting he had been drunk.
During a press briefing on Friday, the spokesperson said that Juncker is taking medication for the condition.
The spokesman said Juncker's ability to do his job was not affected.
The episode has prompted speculation that Juncker had been drinking. "I think it's been a very effective way of negotiating, but I'm not negotiating, I just want fairness for the United States", he said.
It is no secret that Juncker enjoys a drink but he has always hit back at claims that he is an alcoholic. Juncker told the paper he had problems with his left leg, ever since a auto accident in 1989 had left him in a coma for three months and then using a wheelchair for six months.
This is not the first time he has been filmed unsteady on his feet. "I have some difficulties to walk".
Juncker's discomfort led the prime ministers of the Netherlands and Portugal to help him off a stage, while US President Donald Trump and British Prime Minister Theresa May stood and watched.
Juncker, whose five-year mandate as head of the EU's executive arm ends in 2019, is known to use his sense of humour and frankness to achieve compromise in the 28-nation European Union.