Arroyo walked one and struck out five. He threw 91 pitches, most coming in the Astros' seven-run fourth inning.
Reds manager Dusty Baker echoed Ross' concerns regarding Arroyo.
"We're trying to help him figure it out," Baker said. "We don't have any answers. He had better location tonight. But, he didn't have the velocity. I don't think there's anything physically wrong. I hope not. When he gets the ball up, they're not missing it."
Ken Griffey Jr. collected career home run No. 597, and Edwin Encarnacion extended his hitting streak to 13 games with a solo home run in the loss.
The defeat capped off a tumultuous day for the Reds organization.
Earlier Wednesday, Walt Jocketty was named president of baseball operations and general manager. Jocketty, previously a special advisor to Reds CEO Bob Castellini, replaced Wayne Krivsky as GM.
There were no immediate solutions for Arroyo's struggles.
Since joining the Reds, Arroyo has been somewhat of a streaky pitcher, but the right-hander's current stretch is as bad as it gets.
Arroyo is 0-3 with a 7.56 ERA. Wednesday's outing was his shortest since a two-inning stint against the Nationals on May 21, 2007.
Arroyo's rough start is reminiscent of last season, when he started 3-9 with a 4.84 ERA in 18 starts prior to the All-Star break. He finished the season 4-2 with a 3.16 ERA in his final nine starts.
"I feel great physically," Arroyo said. "I just don't have the velocity. It's hard to get any zip on the ball. I need to figure it out, man. There are times you're not going to have your best stuff. I've never had a stretch like this to start the season. I'm just getting beat."
Griffey edged closer to the 600 homer mark in the first inning when he launched a 2-0 pitch from Astros starter Chris Sampson into the right-field stands.
Griffey's solo homer, which traveled an estimated 424 feet, put the Reds ahead, 1-0. It was his 199th home run in a Reds uniform, moving him into sole possession of eighth place on the franchise's all-time home run list ahead of Barry Larkin.
Sampson is the 381st different pitcher off which Griffey has homered.
The lead was short-lived.
Consecutive doubles by Carlos Lee and Hunter Pence produced the Astros' first run, and Mark Loretta's RBI single scored Pence to put Houston ahead, 2-1.
The Astros had runners on second and third with one out, but Arroyo struck out Kaz Matsui and Darin Erstad to end the inning.
Arroyo walked the tight-rope again in the fourth. With runners on second and third with nobody out, Arroyo fanned J.R. Towles and Sampson. But Matsui came through with a two-run single to right putting the Astros ahead, 4-1. Miguel Tejada's RBI single made it 5-1. Lance Berkman followed with a single to right, scoring Darin Erstad to put the Astros ahead, 6-1.
Right-hander Mike Lincoln replaced Arroyo.
Lincoln fielded Pence's slow-roller in front of the mound, but his throw sailed past first baseman Joey Votto and down the right-field line. Pence was credited with a hit. Lincoln was charged with an error, permitting the second run to score and giving Houston a 9-1 lead.
Scoring opportunities were few against Astros starter Chris Sampson, who allowed two runs on eight hits in seven innings in earning his first victory of the season.
Ross, who was reinstated from the 15-day disabled list prior to Wednesday's game, went 2-for-4 with a double.
Corey Patterson's pinch-hit double in the seventh scored Adam Dunn to make it 9-2. It was the first RBI by a Reds pinch-hitter this season.
Encarnacion homered into the left-field stands off right-hander Geoff Geary to cap the scoring.
Four Reds relievers combined for 5 1/3 innings, allowing just one earned run.
But the focus following the game was squarely on Arroyo.
"They're wanting to look for things to see if there's something wrong with me physically, or mechanically," Arroyo said. "Most of the time, I just try to get extra rest and change up my workout. If I can throw 91 when I want to, it's a little bit different game. Tonight, I had 88 at best."