A 27-year-old man was discovered by paramedics suffering from a head injury, but declined hospital treatment.
Around the same time, police and ambulance staff were alerted to a 39-year-old man in the area, who had been stabbed.
The incident happened around 8:50pm on Sunday in the Edinburgh Road area of Penicuik in Midlothian.
Police said they are following a "positive line of inquiry" in relation to the stabbing. However, they are appealing for anyone who may have witnessed anything suspicious in connection with either assault to come forward.