The Padres placed Knehr on the 15-day injured list Wednesday, Kevin Acee of The San Diego Union-Tribune reports.
Knehr was asked to start Tuesday's game on short notice, as Yu Darvish was scratched due to illness. Knehr surrendered five runs over two innings, and he reportedly experienced elbow discomfort toward the end of his start. Ray Kerr is expected to be called up from Triple-A to replace Knehr, and Knehr will be eligible to return immediately after the All-Star break.