White Sox ace Lance Lynn will undergo surgery to repair a small tear in a tendon in his right knee, GM Rick Hahn announced on Sunday. 

Lynn is expected to be unable to throw off a mound for four weeks. After that, he'll require a ramp-up period, which means he might not be able to rejoin the rotation until mid- to late May, barring any setbacks. Lynn also spent time on the injured list last season with inflammation in that same knee. 

Lynn, who turns 35 in May, is a hugely important part of the Chicago rotation. Last season, he pitched to a 2.69 ERA and a 3.91 K/BB ratio in 157 innings -- numbers that resulted in Lynn's second career All-Star appearance and a third-place finish in the AL Cy Young balloting. Over the past three seasons, Lynn owns an ERA+ of 146 with a K/BB ratio of 3.96. 

Lynn's injury and surgery mean that the White Sox's rotation, at least for the early weeks of the season, will consist of Lucas Giolito, Dylan Cease, Dallas Keuchel, Michael Kopech and a fifth starter to be determined. 

Right-hander Vince Velasquez, whom the Sox signed earlier this offseason and who had been ticketed for a long relief role, seems like one possible replacement. The 29-year-old Velasquez has 127 starts across parts of seven big-league seasons. 

In 2022, the White Sox will be looking to win the AL Central for a second straight year and make the postseason for a third straight year. Lynn, to say the least, is vital to those goals.