The man was found opposite the JCT600 garage in Sticker Lane at about 10.57pm on Friday, August 7.
When he was found, he was shirtless and wearing jogger bottoms and was walking in and out of the road.
The man, who is believed to be in his late twenties or early thirties, was taken to hospital.
His condition has worsened and he is now in a critical condition.
Police are keen to establish how he was injured.
Detective Chief Inspector Sharron Kaye, said: "At about 9.50pm on Friday police received reports of a topless man in jogging bottoms walking in and out of traffic in Sticker Lane.
"This man is now in hospital in a very serious way and enquiries are ongoing to establish what has happened to him.
"Our enquiries suggest he was in Parsonage Road and Westbury Street at about 9.30pm, so we would be keen to speak to anyone who may have seen him at that time.”
Anyone with information which may be able to assist the investigation is asked to contact Bradford CID on 101 or via the West Yorkshire Police website.
The log reference is 2373 of 7 August.
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