The 58-year-old was found at a residential site north of Carlisle in Cumbria in a dawn raid on Wednesday by officers from the Gangmasters and Labour Abuse Authority (GLAA).
The potential modern slavery victim was taken by specialist trauma officers to be medically examined and assessed, said GLAA.
A 79-year-old man has been arrested on suspicion of modern slavery offences.
In a statement, GLAA added: “The operation has been supported by specialist officers from the National Crime Agency, the Cumbria Housing Department who are investigating possible health and safety breaches, and officers from Cumbria Police.
“Modern slavery exists in a whole range of forms across the UK. If you suspect someone is being exploited or abused, please do not hesitate to get in contact with us.
“Your call could be the difference between exploitation continuing and worsening or a victim being rescued and given the support that they desperately need.”