``I'll start at six weeks and go from there,'' Diamondbacks manager Torey Lovullo said. ``It could be more. It could be less. Obviously a big blow. Another big blow for us.''
Lamb had an RBI double in the ninth inning of Wednesday's 4-1 loss to the Padres, but pulled up lame heading into second base. He was tended to by athletic trainers before being replaced by a pinch runner.
The third baseman had an MRI on Thursday.
``Obviously, I'm bummed,'' Lamb said. ``It's really frustrating. I was just getting my feet wet and getting back to feeling like a part of the team.''
Lamb played in just 56 games last season due to shoulder woes that eventually led to surgery.
The Associated Press contributed to this report.