Patong Police Station duty officer Pol Capt Jirasak Boonsang said the American’s three friends could not be sure the body was that of Mr Shane.
It will now be sent to the Police Forensic Science Institute in Bangkok for identification as soon as police receive dental and other records from Mr Shane’s family.
Mr Shane, a student majoring in Sustainability at Arizona State University, went missing on Tuesday night after he and three fellow-students went swimming off Patong Beach.
All four got into trouble in the surf, but while the other three were rescued or made it back to shore by themselves, Mr Shane could not be found.
A search for him the following day was called off after five hours.
The students had arrived in Phuket two days earlier on a short-term exchange arrangement, working with Phuket City Municipality.