BOSTON — When Daisuke Matsuzaka arrived in Boston he was hailed as a “national treasure.” As he left the mound in the rain Saturday night, there were a smattering of boos from a fan base frustrated by years of his inconsistency.

And now it looks like we may have seen the end of the Dice-K era in Boston.

More than any pitcher or player in recent Red Sox history, Matsuzaka is as much of an enigma now as he was when he arrived amidst much hoopla in the global baseball community.

It is easy to say Dice-K was a disappointment, and for the past four seasons he has been. He has a 17-20 record with a 5.30 ERA since the start of 2009.

Those are not satisfactory numbers for a pitcher that cost the team more than $103 million for six years of service.

Yet those numbers alone should not be what Matsuzaka is judged by.

Don’t forget that he was 18-3 with a 2.90 ERA in 2008. It was the most major league wins by a Japanese-born pitcher and the lowest ERA by a Sox pitcher since Pedro Martinez’s 2.22 ERA in 2003.

At that point, Matsuzaka was 33-15 with a 3.72 in two seasons. And it seemed his best years were ahead of him.

Yet in 2009 he pitched 591/3 innings, and was plagued by shoulder fatigue all year.

It’s worth noting the Red Sox didn’t get to see Matsuzaka until late in the spring of his third year.

Rather than reporting to camp in Fort Myers, Fla., he began his preseason by working with the national team in Japan to prepare for the World Baseball Classic that March.

Matsuzaka threw 249 pitches in three starts during the WBC that year. This, after throwing deep into the postseason in two straight Octobers.

Matsuzaka was throwing meaningful innings just five months after pitching playoff baseball for the Red Sox. Was the wear and tear of those March games the beginning of the end for Dice-K in the USA?

We’ll never know for sure. But the Red Sox were unable to oversee his throwing regimen that spring, and were unsure what type of workload he was handling in the Japanese training camp.

Before that spring, Boston management had been very careful about bringing Matsuzaka along slowly. Having spent his entire life throwing in the “more is better” philosophy of Japanese baseball, it wasn’t easy for Dice-K to scale back and adjust to the between-starts routine of the American five-man rotation.

The Red Sox felt they had reached a good middle ground with the pitcher, and expected that to continue. It didn’t. Matsuzaka went 4-6 that season, and won just 13 more games over the three seasons that followed. The “national treasure” became a nonvital part of the staff.

Matsuzaka will undoubtedly pitch elsewhere next season, for far less than the $10 million he made with the Red Sox this year. Red Sox fans will long debate his value with this team over the past six years.

The Sox will always wonder what could have been. Would things have turned out differently if he had gone through a normal spring-training routine in 2009? We’ll never know. It’s a philosophical discussion, nothing more.

Just don’t forget how much anticipation surrounded the mysterious Matsuzaka when he first arrived.

He’s just as mysterious now, but no one is anticipating his return to the team.

Tom Caron is the studio host for Red Sox broadcasts on the New England Sports Network. His column appears in the Press Herald on Tuesdays.