Jeremy Corbyn was spotted at a rail strike picket line on Thursday sporting a black eye and a split lip.
The former Labour leader said he sustained the injuries on Wednesday when he tripped over a tree root while out jogging.
“I was out running in Finsbury Park and, unfortunately, a tree root had protruded over the path," Corbyn said outside Euston station.
“Me and the tree root collided and I collided with the ground afterwards. There was nobody else involved – totally me on my own – but I love running anyway.”
Corbyn, who is now an independent MP, has been a vocal supporter of strike action.
At the picket line he said Labour MP Sam Tarry’s treatment had been “very unfair” after he was sacked from the shadow front bench after he joined striking workers at a picket line in July.
“Sam is a trade union person like me, he used to work for the TSSA, he went on a picket line to support his union and his members," said Corbyn.
“I think to dismiss him from his shadow position was very unfair.”
It comes as unions warn of strikes lasting "indefinitely" over disputes concerning pay and working conditions.
Mick Lynch, general secretary of the Rail, Maritime and Transport union (RMT), has called on the government to engage with negotiations.
"Instead of waging an ideological war against rail workers, millions of voters would rather that the government allow for a fair negotiated settlement," said Lynch.
However, the government has criticised strikers for disrupting the lives of the public.
“It’s clear strikes are not the powerful tool they once were and union chiefs are no longer able to bring the country to a standstill as, unlike them, the world has changed and people simply work from home," said a spokesperson for the department of transport.
“All these strikes are doing is hurting those people the unions claim to represent, many of whom will again be out of pocket and forced to miss a day’s work.
“We urge union bosses to do the right thing by their members and let them have their say on Network Rail’s very fair deal, which will deliver the reforms our rail system urgently needs.
“It’s time to get off the picket lines and back around the negotiating table – the future of our railway depends on it.”
Watch: Network Rail warns disruption caused by strikes will be 'significant'