A 65-year-old woman and a 25-year-old man have been arrested on suspicion of encouraging or assisting a suicide.
Sussex Police confirmed the pair were arrested in the Chichester area and it has been reported that they had planned to accompany a 71-year-old man to Switzerland to end his life.
Police are investigating to see if the man is able to decide to travel himself.
A Sussex Police spokesperson said: “The investigation is looking into what steps, if any, the suspects had made in taking the man out of the country.
“If it is confirmed the man had the mental capacity to make decisions for himself then we would not be able to prevent him travelling.”