Knehr was optioned to Triple-A El Paso on Saturday, Kevin Acee of The San Diego Union-Tribune reports.
Knehr joined the Padres' bullpen last week after active rosters expanded to 28 players, but he gave up four runs on four hits and two walks while striking out two in 1.2 innings during his lone appearance following his promotion. He'll head back to the minors since Pierce Johnson (elbow) is expected to be reinstated from the 60-day injured list Saturday.