The Rangers and veteran slugger Lance Berkman have agreed on a one-year contract for $11 million that makes him their designated hitter in 2013.

The deal, pending a physical, includes a $1 million buyout and a vesting option for 2014 that kicks in if he collects 525 to 550 at-bats, said a major-league source.

The move gives the Rangers a proven bat in the middle of the lineup to help make up for what was lost when Josh Hamilton signed with the Angels. But the deal will be a bust if Berkman can't stay healthy.

Berkman had surgery on his right knee in May while with St. Louis and again in September as the Cardinals were pushing for the postseason. He has had four operations on his right knee during his career, which started in 1999.