Liechtenstein international Buchel, 27, did not make a first-team appearance for the U's last season and spent time on loan at League Two Barnet.
Shearer signed a 12-month contract on Tuesday after being released by Mansfield Town.
Midfielder Josh Ashby, 21, has signed a new one-year deal while he recovers from a knee injury.
Goalkeeper Benjamin Buchel has left Oxford United following the arrival of Scott Shearer.