"Well, I don't know if it was timing," Baker said Monday. "Sometimes, there's necessity. How many other guys do we have on the [40-man] roster? Anybody else we'd have to put on the roster."
Bailey, 22, was 4-4 with a 4.15 ERA in 12 starts for Louisville this season. He allowed 66 hits, 32 earned runs and 31 walks with 55 strikeouts over 69 1/3 innings.
But there have been some issues for Bailey keeping the ball in the strike zone. During a recent three-start stretch, he had a 9.42 ERA with 21 hits and 13 walks. There was improvement on May 27, when Bailey worked six innings and allowed just one earned run at Toledo.
In his last outing for Louisville on Sunday, Bailey worked an abbreviated 2 2/3 innings and gave up two earned runs and three hits. He was removed and given word he was going back to the Majors.
"Some reports have been excellent," Baker said. "And some reports have been similar to what he struggled with before -- his consistency."
Bailey will be the latest of the elite prospects to join the 2008 roster behind Joey Votto, Edinson Volquez, Johnny Cueto, Paul Janish and most recently, Jay Bruce.
"So far, so good calling up young guys," Baker said.
The organization's top pitching prospect, Bailey made his much anticipated Major League debut on June 8, 2007, before he went 4-2 with a 5.76 ERA in nine starts.
Bailey contended for a rotation spot during Spring Training but was a late cut after being inconsistent with his control.
Thursday will be the second time Bailey has pitched at Citizens Bank Park. On June 26 of last season, he lasted only 1 2/3 innings and gave up six earned runs in an 11-4 Reds loss to Philadelphia.