Cueto, 32, wrote "my horse Popeye died" for the caption on the photo, which showed the animal on its side in the grass.
The pitcher owns a 500-acre ranch in his native country, the Dominican Republic, where he also tends to cows, chickens and goats. He posted several more videos and images of Popeye, before his demise.
This isn't the first time Cueto has posted a photo of one of his dead horses. This also isn't the first time he has lost a horse named Popeye. The pitcher also posted a photo of another Popeye after that horse died in 2016.
Cueto posted a 3.23 ERA and a 3-2 record in nine starts last season. The two-time All-Star has a 3.45 ERA with a 29-15 record on the hill in three seasons with the Giants. He joined the franchise in 2016. Cueto is set to make $21.8 annually through 2021. The Giants have a $22 million option for Cueto's services in 2022, with a $5 million buyout.
Giants pitchers and catchers report to spring training on Thursday in Scottsdale, Ariz. Cueto is expected to miss the entire season after undergoing Tommy John surgery in August.