McCartney becomes the second receiver to leave West Virginia in a a short span, joining junior Tavares Copeland who quit the team last week.
Mountaineers' head coach Dana Holgorsen did not give any further explanation on Monday as to why McCartney had left the program.
Before leaving, McCartney had nine catches for 112 yards in his first season with West Virginia.
The Mountaineers lost, 55-34, to the Oklahoma St. Cowboys on Saturday. After starting the season 5-0, West Virginia has lost four consecutive games and slipped to seventh in the Big 12. West Virginia has three games left on their schedule to try to gain bowl eligibility, starting with a visit from the No. 12 Oklahoma Sooners this Saturday. That game will be televised on FOX and is scheduled to kick off at 7 p.m. ET.