Green’s Dictionary of Slang

(orig. US) small-scale, modest.

1902		C.L. Cullen More Ex-Tank Tales 54: I didn’t feel like standing for that – not from any Class Y, minor league town like Cincinnati.
1947		B. Schulberg Harder They Fall (1971) 33: I was a little surprised that Nick [...] would get himself involved with a minor league thief.
1953		A.J. Liebling Honest Rainmaker (1991) 5: That then distinctly minor-league city.
1959		H. Ellison ‘Sally in Our Alley’ in Gentleman Junkie (1961) 119: I felt like a minor-league Herbert Philbrick, spying on all my friends.
1977		W.D. Myers Mojo and the Russians 21: ‘This turkey’s little skirmish with Drusilla Gorilla is minor league in the big ball game of L-I-F-E’.
1989		T. Blacker Fixx 46: There are more than a few minor-league achievers all over the world.
2000		S. Maloney Big Ask 164: But Jack Butler was a minor-league player [...] he represented no threat.