The 24-year-old man was taken to hospital from the site near Haringey where National Grid are tunnelling as part of the London Power Tunnels project.
Costain is main contractor on the job and the injured man was working for a subcontractor.
A National Grid spokesman told the Enquirer: “A worker was injured at our Eade Road construction site in Haringey at approximately 6am today.
“The individual has received medical treatment and is recovering in hospital.
“Our thoughts are with our colleague and we wish him a prompt recovery.
“Health and safety is of paramount importance to us.”
The spokesman said work had been temporarily suspended at the site while the accident is investigated.