On Wednesday, Victor Martinez turned 37 years old.

He has had two major knee surgeries and is coming off the worst season of his career. But this coming season, the Tigers will again lean heavily on Martinez in the middle of their batting order, with their fingers crossed that he can regain the health that made him the American League's Most Valuable Player runner-up in 2014.

"He is definitely a key person," general manager Al Avila said last month. "Because without him, it would be hard to protect (Miguel Cabrera) in the lineup. So yeah, at the time we gave him the contract we gave him, we thought he was a very important key in that lineup and he still is, there's no doubt about that."

Martinez hit .245 with 11 home runs and 64 RBIs in 120 games in 2015. He was hampered for the duration of the season by left knee soreness stemming from the meniscus tear he suffered late in the off-season.

By all accounts, Avila said, Martinez is healthy and undergoing a normal offseason workout regimen in Florida.

In 2014, Martinez hit .335 with 32 home runs and 103 RBIs, and the Tigers rewarded him with a four-year, $68 million contract that runs through the 2018 season, when he will be 39.

"The heart of our lineup is J.D. Martinez, Victor Martinez, Ian Kinsler and Miguel Cabrera," Avila said. "Those guys are the key."

But the biggest key is Victor Martinez, their cleanup hitter, and keeping him healthy so he can pack the punch needed to power the middle of the lineup.