He was also arrested today on suspicion of robbery in October 2009. The man was arrested at a residential address in Camden at 10:00hrs.
He has been taken to a north London police station where he will be interviewed by detectives.
Dr Farooq, aged 50, was on his way home from work when he was attacked in Green Lane, shortly before 17:30hrs on Thursday, 16 September. He was found suffering from stab wounds and head injuries.
Detectives believe there are other people who may hold vital information about the attack and continue to urge them to come forward. They still want to trace two men and speak to them in connection with the incident.
Officers have previously issued an e-fit of one of the men. The man is of Asian appearance, aged in his late 20s or early 30s, 5ft 4ins to 5ft 6ins tall, of slim build, with piercing eyes, a pointed, pale-skinned face, short black/dark coloured hair, and a goatee-style beard. He was wearing a dark coloured baseball-style cap.
The second man is also Asian. He is aged in his 30s, of stocky build, 5ft 9ins to 5ft 11ins tall, with short black hair.