Dr Sara Hanna, who is part of the senior management team at Guy's and St Thomas', said: "I am really worried about next week. I am particularly worried about ability to staff our rotas. I am hopeful we will have enough doctors but can't say for sure.
"It is impossible to say there won't be harm to patients. Junior doctors are an incredibly important part of the workforce."
Why are doctors demanding the biggest pay rise?
Doctors want up to £262 an hour to cover strike
Junior doctors represent more than 40% of the medical workforce and include those fresh out of university through to experienced medics with more than 10 years of experience. Around two-thirds are BMA members.