"While McCullum endured a strain in his left hamstring during fielding against Delhi Daredevils on May 4, Nathu suffered back spasms during the Lions' home game in Rajkot against Kings XI Punjab.
"Nathu hasn't played a match since then," the IPL franchise said in a statement on Friday.
"The New Zealander has been advised three-four weeks of intensive rehabilitation so as not to aggravate the damage in his hamstring," the statement added.
McCullum has scored 319 runs at a poor average of 29 in the 11 matches he has played so far in this year's IPL. His highest score was 72.
Nathu has struggled to find a place in the playing XI this season. He has played only two matches and has claimed just one wicket.
Source - Agency