Aroldis Chapman's average fastball on Monday was 95.37 mph, his lowest of the season. (AP)

Monday night there was something odd in Cincinnati -- pitching in the 10th inning, Aroldis Chapman's fastball was in the low 90s. For a guy who has recorded the fastest fastball in baseball history, the low 90s is usually reserved for his offspeed pitches.

Chapman is still averaging 98.3 mph on his fastball, but he didn't help that on Monday, when his fastest pitch was 97.1 mph.

A fastball of 97.1 mph is usually cause for celebration, but for Chapman, it's a cause for concern. On Tuesday, Reds manager Dusty Baker said he was giving his closer a rest for a couple of days.

"It will at least be a couple of days," Baker told reporters (via MLB.com). "If not, it wouldn't be a rest. We need him for the next six weeks, hopefully."

Following Monday's game, Baker said the team doctor had examined Chapman and saw nothing physically wrong with him. Despite what Baker called, "shoulder fatigue," Chapman has only pitched twice in the previous six days and hasn't pitched in back-to-back games in two weeks. Chapman said Tuesday that he felt no pain in his arm.

"A little of bit of fatigue," Chapman told reporters through a translator, Tomas Vera (via the Cincinnati Enquirer). "For a couple games back, I feel like I haven't been myself. I felt a lot of fatigue. I don't think it’s anything major. I just feel weak."

Here's a look at his last month of outings from the indispensable Brooks Baseball, focusing on his fastball velocity:

Sept. 10 vs. Pirates -- 12 fastballs, 95.37 average, 97.1 max
Sept. 7 vs. Astros -- 14 fastballs, 97.03 average, 98.3 max
Sept. 4 vs. Phillies -- 19 fastballs, 98.01 average, 99.7 max
Sept. 2 vs. Astros -- 13 fastballs, 97.62 average, 99.5 max
Aug. 28 vs. Diamondbacks -- 11 fastballs, 97.36 average, 99.5 max
Aug. 27 vs. Diamondbacks -- 10 fastballs, 96.46 average, 97.4 max
Aug. 22 vs. Phillies -- 17 fastballs, 99.02 average, 101.3 max
Aug. 21 vs. Phillies -- 9 fastballs, 99.71 average, 102.3 max
Aug. 19 vs. Cubs -- 9 fastballs, 98.04 average, 99.9 max
Aug. 18 vs. Cubs -- 21 fastballs, 97.51 average, 100.3 max
Aug. 17 vs. Cubs -- 7 fastballs, 97.13 average, 98.5 max
Aug. 12 vs. Cubs -- 14 fastballs, 99.81 average, 101.1 max
Aug. 11 vs. Cubs -- 9 fastballs, 101.32 average, 102.7 max
Aug. 10 vs. Cubs -- 19 fastballs, 97.72 average, 101.5 max

Here's his average fastball over the course of the season (also from Brooks Baseball):

April -- 167 fastballs, 96.90 mph average
May -- 194 fastballs, 97.68 mph average
June -- 186 fastballs, 98.49 mph average
July -- 207 fastballs, 99.92 mph average
Aug. -- 156 fastballs, 99.73 mph average
Sept. -- 58 fastballs, 97.14 mph average

It wasn't just velocity, it was location. Chapman walked three of the five batters he faced on Monday, throwing 15 balls and seven strikes. Coming into the game, he'd walked just 17 batters in 67 innings, so the three walks were as startling as the lack of velocity. That worry was compounded by his first blown save in 28 appearances on Friday.

The Reds rested Chapman in late July, after his blown save against the Twins, giving him five games off between his ninth save on June 26 and appearing against the Dodgers on July 2. He then got another four days off before his next appearance, July 7 against the Padres. Against the Brewers on June 26, he threw 14 fastballs at an average of 97.43 mph. After the rest, on July 2, he threw 14 fastballs against the Dodgers, averaging 100.11 mph. Chapman told reporters he expected five days to a week rest this time, and thinks that should do the job.

With 20 games remaining and a 9 1/2 game lead in the NL Central entering Tuesday's game, if the one thing the Reds can afford to do right now its to give Chapman a rest, especially with Jonathan Broxton and Sean Marshall already in that bullpen.

For more baseball news, rumors and analysis, follow @EyeOnBaseball on Twitter, subscribe to the RSS feed and "like" us on Facebook.