Jalen Mills’ injury is more severe than first thought.

Mills, a senior starting safety, had surgery on his injured lower leg, coach Les Miles said on Tuesday. A source said the surgery pushes back the timeline for his return to “at least” six weeks, likely putting Mills available, at the earliest, for the Oct. 10 against South Carolina.

Mills needed a small rod inserted in the leg, a source said. Miles declined to go into details about the surgery of the timeframe for his return.

“I’m still harboring personal feelings that we can get him back sooner rather than later,” Miles said. “We don’t know exactly how soon [he’ll return].”

Mills’ mother told The Advocate last week that her son would miss two games and would not need surgery. That changed over the last few days, pushing back the comeback of one of the Tigers’ most experienced players.

Mills started all 39 games of his first three years at LSU before suffering the injury at an Aug. 19 practice when a lineman fell on his ankle.

A source told The Advocate last week that Mills would miss at least the first two games, but coaches were hoping he could return for the Game 3 match against Auburn on Sept. 19.

Rickey Jefferson is expected to replace Mills at safety – something he already did often during last season. In the Tigers’ five-defensive back set, Mills moved from safety to nickel back, and Jefferson replaced him at safety.

The Tigers play nickel – the five-DB set – just as much, or more, as their base 4-3 defense in some games. Dwayne Thomas says he’ll be replacing Jefferson at nickelback.

Follow Ross Dellenger on Twitter @DellengerAdv.