Police are appealing for the driver of a tipper lorry to contact them after it was involved in a collision with a cyclist but failed to stop.
The crash happened on the A6094 between Howgate and Leadburn at 0840 BST.
The cyclist, a man in his 40s, was seriously injured and is being treated at the Edinburgh Royal Infirmary.
Police said the driver of the lorry, which had a black or blue tarpaulin cover, may not have realised he had been involved in a collision.
Following the incident the lorry continued towards Leadburn.
The road was closed for a short time while investigations were carried out at the scene.