Banks' time with the Astros was brief, being called up to start Saturday's game in place of injured started Felipe Paulino.
The Astros have 10 days to trade him, release him or outright him to the Minor Leagues.
The move likely means veteran Brian Moehler will keep his spot in the rotation for the time being. Moehler threw five innings and allowed two earned runs Saturday for his first win this season. He's 1-4 with a 5.63 ERA in 18 games, including six starts.
Bud Norris, on the disabled list since May 24 with bursitis and biceps tendinitis, will rejoin the rotation on Monday in Milwaukee. He's 2-5 with a 6.80 ERA in nine starts with the Astros and posted a 3.06 ERA in three rehab starts at Triple-A Round Rock.
Banks gave up eight hits, four walks and six earned runs in four innings Saturday. He was 8-5 with a 2.97 ERA in 15 starts this year at Round Rock.