Homer Bailey hasn't pitched for the Reds in 15 months.
On Tuesday the Reds activated Bailey on Thursday after seinding down OF Kyle Waldrop after the game on Wednesday. The Reds also placed RHP Caleb Cotham on the 60-day disabled list.
Bailey could pitch Sunday in San Diego.
He got up to 95 pitches on Tuesday, his last rehab start.
Bailey pitched 5 2/3 innings against Milwaukee on the 23rd last year, allowing two earned runs.
Bailey made 23 starts in 2013 and had a 9-5 record with a 3.71 ERA. He has made just two starts since August 7, 2014.