To this point, Arroyo (1-1) has been healthy and thus has pitched well.
But a troublesome cranky back acted up prior to his last start, maybe or maybe not prompting an old nemesis, the home run ball, to reappear.
Arroyo battled through a bout with mononucleosis during Spring Training last year and later developed a sore lower back, factors in the right-hander giving up a club record and National League-leading 46 homers.
He gave up only two homers in his first four games this season, but now Arroyo's back is a concern again after he gave up two in a 3-1 loss to the Cubs in his last start on Wednesday.
"It felt pretty good, but it has been bugging me," Arroyo said after the game. "I went the entire offseason trying to keep it healthy, but then it started to tighten up on me during the St. Louis start (on April 19). It was really bad two starts ago, and a little better the last time.
"It's something we're trying to keep in check, but it's hard, because you don't know what's causing it."
When he is healthy, Arroyo usually is good, as his 3.03 ERA, 1.19 WHIP and 18:3 strikeouts-to-walks ratio this season attests.
Arroyo will be opposed on Monday by right-hander Marco Estrada, who will start for the first time since April 28, meaning that he'll go nine days between outings instead of the usual four. This will be his third game in place of injured lefty Chris Narveson, who is out for the season.
Reds: Bruce slugging away
Jay Bruce was 1-for-4 on Sunday against the Pirates, leaving his season average at .300. His slugging percentage is .630, third in the National League behind the Dodgers' Matt Kemp (.825) and the Cubs' Bryan LaHair (.767)
Brewers: Filling up the disabled list
Shortstop Alex Gonzalez was placed on the disabled list Sunday after sustaining a knee injury sliding into second base in Saturday's 5-2 loss to the Giants. The makes it three Brewers in three days to suffer the same fate.
Outfielder Carlos Gomez was placed on the 15-day disabled list earlier Sunday, retroactive to Saturday, with a strained left hamstring, while first baseman Mat Gamel was transferred to the the 60-day disabled list after going on the 15-day DL Friday with a torn ACL in his right knee.
Asked before Sunday's game if he would consider batting Bruce fourth in place of the struggling Brandon Phillips to spark the offense, Reds manager Dusty Baker said: "No because I want to break up those lefties. Bruce is hitting well and hitting home runs, but he still is improving at driving in runs himself. You can only put so many things in a bag."
Phillips went 0-for-4 in Sunday's 5-0 win over the Pirates and his average fell to .215.