Originally written and recorded by the Bee gees I have no idea how many cover versions have been made.Below are a small sample
P. P. Arnold (1968)
I Califfi (1968)
Gary Puckett & the Union Gap (1968)
The Sweet Inspirations (July 1968)
Eric Burdon & The Animals (December 1968)
Nina Simone (1969)
Janis Joplin (October 1969)
Roberta Flack (November 1971)
Kim Carnes (December 1971)
The Flying Burrito Brothers (1973)
Hank Williams Jr (1979)
Bonnie Tyler (?)
Jimmy Somerville (1990)
Michael Bolton (1992)
Slobberbone (2002)
However, according to wikipedia
Yesterday" is a pop song originally recorded by The Beatles for their album Help! (1965). According to the Guinness Book of Records, "Yesterday" has the most cover versions of any song ever written, while BMI asserts that it was performed over seven million times in the 20th century alone. The song remains popular today with more than 3000 recorded cover versions, the first hitting the United Kingdom top 10 three months after the release of Help!. Some sources still assert that White Christmas by Bing Crosby has more cover versions