Lambert was sent to Triple-A Albuquerque on Monday, Patrick Saunders of The Denver Post reports.
Lambert held his own in big-league camp, compiling a 3.38 ERA and 1.28 WHIP across 13.1 innings, but will return to the minors to open the season. The right-hander owns a career 3.76 ERA across parts of four seasons, though he struggled to a 5.04 ERA and 1.57 WHIP in his first taste of Triple-A last year (11 starts, 55.1 innings).