Police were called to Kirkgate, Huddersfield, at around 12.40am today (Sunday).
A man, in his 30s, was found with a serious head injury and taken to hospital, where he remains in a critical condition.
Police believe he was assaulted outside the nearby McDonald's restaurant.
Two teenagers, aged 15 and 16, have been arrested on suspicion of assault.
Anyone with information is asked to call police on 101, quoting log 75 of October 1.