The incident took place in the fourth over when the left-hander missed an intended pull off an 89 mph delivery from Wood that hit him on the left elbow.
Imam fell to the ground and winced on the turf in agony.
The 23-year-old then had several minutes' treatment before retiring hurt on three.
?? - "Ouch, ouch, ouch!"— Sky Sports Cricket (@SkyCricket) May 17, 2019
No wickets for England yet but Pakistan have lost a batsman with Imam-ul-Haq having to retire hurt after being struck by a bouncer from Mark Wood...
Watch #ENGvPAK live on Sky Sports Cricket now or follow online: https://t.co/zxTLGxaDZK pic.twitter.com/iKeqna3Cr9
According to a PCB statement, Imam has been taken to hospital for a 'precautionary' x-ray. Further updates will be provided after the x-rays,