The rider, on a lime green bicycle, crashed with the National Express West Midlands bus in Bloxwich Road, Bloxwich, in Walsall just before 4pm on Thursday.
A large cordon was set up in the road after the bike became stuck underneath the bus, which had sustained a smashed windscreen.
The cyclist’s clothing could also be seen on the road behind the bus.
A spokesman for West Midlands Police said: "The road was opened by 7pm last night. No arrests. The driver is assisting with our enquiries.
"The cyclist remains in hospital with possibly life-changing injuries."
Witnesses or anyone with information are asked to call police on the non-emergency 101 number.
Alternatively, details can also be passed on anonymously by calling the Crimestoppers charity on 0800 555111.