BOSTON – Nomar Garciaparra’s first trip back to Fenway Park as an opposing player may end up being his last.

 Garciaparra, who went 2-for-4 as the Oakland A’s designated hitter Monday night, said he “was on the verge of retiring in the off-season last year,” due to a series of debilitating injuries in his third season with the Los Angeles Dodgers. Hand, knee and calf injuries limited the first baseman to 55 games.

 He chose to return to the American League, however, and signed a one-year, $1-million deal with Oakland as what he calls “a part-time player.” He’s appeared in only 32 of the A’s 81 games thanks to twice landing on the disabled list with a strained right calf. That makes five DL stints in two years and 14 in his career.

 In an interview before his return last night against the Red Sox, Garciaparra said he’s been diagnosed with a “genetic condition’’ that limits his body’s recovery time from injury. The condition is called chronic extertional compartment syndrome, which causes excess scar tissue to develop at the injury site and limits rehabilitation and increase the likelihood of additional injury.

 “I have a genetic condition that I was born with. I found that out last year,” said Garciaparra, who’ll turn 36 this month. “I spent so much effort and time on my body and to finally hear that it was nothing I did or nothing I could’ve prevented, it’s just what I have.”

 Now in his 14th major-league season, Garciaparra said he’s “relieved’’ to learn of the medical issue and is treating it daily.

 “Now that I know I have it, I’m pretty grateful that I’ve come this far. I’m grateful for everything I’ve been able to experience,” he said.

 Garciaparra contributed greatly in Oakland’s 6-0 shutout of the Red Sox Monday. He singled in the A’s first run with a ground ball to left field and also smacked a single past the third-base bag in the eighth inning. It’s just the fifth time all season he’s racked up more than one hit in a game.

 Injuries are nothing new to Garciaparra. Before a major groin injury with the Cubs in 2005, he was sidelined for 81 games in 2004 when he was with the Red Sox and Cubs. He had problems that season with his Achilles tendon, left wrist and right groin. He had surgery on his right wrist when he was with the Red Sox in 2001 and played in a career-low 21 games.

kmcnamar@projo.com