The incident was captured in a photo Saturday.
The man was traveling from Nice, France to Luton, England. The flight was delayed for about 11 hours.
EasyJet said the airport employee does not work for the airline.
"It was awful the whole thing. I just can't believe people can behave like that," fellow passenger Arabella Arkwright told CNN.
She said her husband was the one who restrained the attacker while they waited for police to arrive.
"We had a serious problem with someone of staff from our subcontractor Samsic," Jean-Franois Guitard, a director at Nice airport told CNN.
Guitard said the passenger complained about the delay to a Samsic employee but when that employee was unable to answer the passenger's questions, he lashed out with a punch to the dad's face.
Guitard said the employee has been suspended.
EasyJet released a statement about the incident:
"We are concerned to see this. It is not an EasyJet staff member, and they do not work for our ground handling agents."
We are concerned to see this - it is not an easyJet staff member & they do not work for our ground handling agents. 1/2— easyJet Press Office (@easyJet_press) July 30, 2017
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