The 22-year-old was being held on suspicion of assault, the Daily Mirror reported.
The 40-year-old victim was discovered shortly before 5 a.m. next to the A66 in Middlesborough in northern Yorkshire. A section of the highway, which runs across northern England from Middlesborough to Cumbria, was closed for several hours while police searched for the missing body part.
The man was hospitalized.
"Officers are keeping an open mind as to how he received his injuries and key to this will be speaking to the man himself when they are able to do so," a spokesperson for Cleveland Police said in a statement.