Jones suffered another injury Saturday against Notre Dame as coach Mark Dantonio said the senior injured his medial collateral ligament and will be out six weeks.
"I normally don't talk about unless they are long-term injuries," Dantonio said Sunday night during his weekly teleconference. "Jairus has an MCL right now, so we are going to lose him for the next six weeks."
Jones was starting in place of injured linebacker Taiwan Jones, who came on once Jairus Jones left injured in the first quarter.
Isaiah Lewis, like Taiwan Jones, wasn't starting against Notre Dame because of an injury.
Dantonio said Lewis had surgery on his meniscus the Thursday leading up to the Youngstown State game.
"With Isaiah Lewis, Isaiah had meniscus surgery last Thursday – the Thursday before – to take out a piece of his meniscus because his knee locked up," Dantonio said. "He was able to get back to practice with us on Wednesday. We need him for the Big Ten season."
Dantonio said MSU wasn't sure if it would have Lewis back based on recovery time, but he played at the fifth defensive back spot against the Irish.
"I thought he played pretty well and he probably could have played in the game at safety, but we just felt like we needed to hold him," Dantonio said. "R.J. Williamson is a very good player, he is basically a starter for us and I thought he had a good game as well."
Williamson started for Lewis for the second straight week and had a team-high 10 tackles.