But Juncker's spokesman said on Friday that the 63-year-old had been suffering from a bad case of back pain and hit back against reports about the Commission president's supposed alcoholic proclivity.
The European Union leader was seen stumbling, walking awkwardly and losing his balance several times ahead of a gala dinner Wednesday.
"The president Wednesday night suffered from a very particularly painful attack of sciatica accompanied by cramps", EU Commission spokesman Margaritis Schinas told a daily briefing as cited by AFP.
Schinas said Juncker, whose term will end in 2019, was taking medication and would be fit enough to attend upcoming meetings and events in China, Japan and Spain.
The spokesman said Juncker's ability to do his job was not affected.
Juncker has previously blamed the unsteadiness on sciatica, which can cause numbness or weakness of the legs.
The episode has prompted speculation that Juncker had been drinking.
"I don't think this is elegant and I don't think this is fair", he added. Juncker told the paper he had problems with his left leg, ever since a vehicle accident in 1989 had left him in a coma for three months and then using a wheelchair for six months. "I have some difficulties to walk. I have sciatica. I would prefer to be drunk", he said of the condition in an address at the Irish parliament last month.
"The president wishes to thank publicly Prime Ministers Mark Rutte and António Costa for assisting him during this painful moment".
Trump, who is set to host European Commission President Jean-Claude Juncker in Washington this month, repeated his line that the EU was treating the United States unfairly on trade, shutting out US farmers.
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