The 29-year-old, who has struggled with injuries since joining the club in September, has not made a single appearance for the first team.
"There isn't much opportunity for him to play and there was a very good opportunity to go to Castres and play," Cockerill told BBC Sport.
"Where that leaves us moving forward long term we will have to see. We may or may not have been in the position to offer him a contract for next season so the right thing to do from his end was to give him the opportunity to go and play and get himself a contract for the foreseeable future."
Leicester currently sit in third place in the Aviva Premiership.