The police were called to Strand just before 8pm yesterday (July 2).
Officers and ambulance crews found a 22-year-old with a serious head injury following an alleged assault.
He was taken to hospital where his injuries were deemed to be neither life-threatening nor changing.
A man was arrested on suspicion of grievous bodily harm by the British Transport Police.
Detectives are appealing for information with witnesses asked to call 101 using reference 8172/2Jul.
A British Transport Police spokesperson said: “Police were called at 19:56hrs on Wednesday, 2 July to reports of an assault outside a supermarket on The Strand.
“Officers joined London Ambulance Service and police partners at the scene where a 22-year-old man had been seriously injured in an alleged assault.
“He remains in hospital where his injuries have been said to be non-life-threatening or non-life-changing.
“A man was arrested on suspicion of GBH by British Transport Police.”
“Enquiries continue.
“If you were a witness or have any information which might help, please call police on 101 with the reference 8172/2Jul.”
A London Ambulance Service spokesperson said: “We were called at 7.52pm on Wednesday 2 July to reports of an assault on the Strand, WC2R.
“We sent an ambulance crew to the scene.
“We treated a man for a head injury and took him to a local hospital.”