Randy Wolf put together a 4.26 ERA in five Cactus League starts for the Mariners. (Darron Cummings/AP)

PHOENIX -- The D-backs signed veteran free-agent lefty Randy Wolf to a Minor League contract on Friday.

Arizona general manager Kevin Towers said Thursday that the team was close to signing an experienced pitcher to provide some depth.

D-backs starters have struggled early in the season, and that has the D-backs looking at alternatives.

Wolf signed a Minor League deal with the Mariners this past February, but he requested and was granted his release by the club after disagreeing with a "45-day consent release" Seattle asked him to sign, which would have made it possible for the team to release him or send him to the Minors within the first 45 days of the season.

"I principally objected to that, simply because we negotiated in good faith in February on a very team-friendly contract if I were to make the team," Wolf said. "I felt like I came in in amazing shape, I pitched great, I earned a spot on the team. They told me I earned a spot on the team and, to me, that advanced-consent thing is kind of renegotiating the contract. So I told them I wouldn't sign it. I disagreed with that."

Wolf, 37, didn't pitch in the Major Leagues last year because of Tommy John surgery, but he's 132-117 with a 4.20 ERA in 376 appearances (368 starts) over parts of 14 seasons. Wolf last pitched in the Majors in 2012, when he logged a 5.65 ERA in 30 appearances for the Brewers and Orioles.

Wolf was originally selected as a second-round pick in the 1997 First-Year Player Draft by the Phillies, and he spent the lion's share of his career in Philadelphia. The left-hander went 69-60 with a 4.21 ERA in 194 games (190 starts) for the Phils, and he was named a National League All-Star in 2003.