(CNN) -- Japanese star pitcher Masahiro Tanaka is only 25. He just pitched a perfect 24-0 season with a 1.27 ERA. For non baseball fans, that's unbelievable form.
It's thanks to this form that he's signed a seven-year, $155 million contract with the famous New York Yankees -- a young player with the best years of his career ahead of him.
But some U.S. baseball watchers are skeptical. The reason? Tanaka has thrown a worryingly high number of pitches.
According to Sports Illustrated's Tom Verducci, Tanaka has thrown more innings at a young age than anybody in the major leagues in few decades. As a pro, the Japanese star had thrown 1,315 innings by age 24, a number unrivaled by virtually any young player today.
Even as a high schooler Tanaka was a powerhouse: during Japan's Koshien Tournament he set a national record with an astonishing 742 pitches in 6 games.
Unlike in American baseball, where pitchers are often warned that throwing too many times leads to early injury, Tanaka has played for years in a Japanese sporting culture that values repetition as a way to achieve perfection.
"The [Japanese] philosophy is repetition, hard work: If I put in more, it's going to make a better pitcher and it's going to take care of everything," explained Japan-based pitching instructor Lyle Yates, to MLB Network Radio.
"It's not in my opinion always focused properly, and the body does need recovery time," he added.
Today, few American pitchers exceed 100 pitches in a game. Yet in a recent game in Japan, Tanaka threw 160 pitches - and topped it off with another 15 pitches the very next day.
Yankees general manager Brian Cashman acknowledged in a conference call with reporters there were "concerns" about those two games. "But with his age, his talent and the scouting assessment, and with the pitching market the way it is, we were willing to take the risk," he said.
Reaction on social media was divided.
"Yankees overpaid for Tanaka 1300+ innings and he's only 24. That's got Tommy John written all over it," wrote Twitter user @Derick_Anderson, referencing the nickname for the elbow surgery first undergone by former major league pitcher Tommy John.
"Tanaka's usage isn't that much different than prospects or even major league pitchers of similar pedigree and age. He will be fine," argued Twitter user @bkblades.
In the end, it's clear Tanaka is ready to prove his own worth.
"I cannot speak English, but I would like to appeal with my performance," Tanaka told reporters in Japan Thursday. "I hope I can perform what I have built up so far on the pitcher's mound."