The incident happened at around 12.10pm on Thursday, May 25, near Greenlaw.
A 67-year-old man came off his Harley Davidson motorcycle and sustained a serious head injury.
He was taken to the Royal Infirmary of Edinburgh where he remains in a critical condition.
Road Policing Officers responded to the scene and the road was closed for around six and a half hours while they conducted inquiries.
Anyone with information in relation to this matter is asked to come forward.
Inspector Richard Latto said: “We are satisfied that no other vehicles were involved in this incident, but our inquiries to establish exactly what happened are continuing.
“I would urge any other motorists who were on the A697 on Thursday afternoon and witnessed the rider coming off his motorcycle, or who have any other relevant information, to contact police immediately.”
Those with information can contact the Road Policing Unit at Galashiels via 101 and quote incident number 1501 of May 25.