The 27-year-old England flanker has been ruled out for the rest of the campaign after suffering ligament damage during last weekend's win over Worcester Warriors in the Aviva Premiership.
"It's horrendous bad luck for Tom because it is only last year that he came back from a very bad neck injury and did so well for England but the Lions as well, but these things happen," Cockerill told the Daily Mail.
"Tom will make a full recovery but it's his season over. It's a blow but we have just got to get on with things."
Leicester continue the defence of their league title on Saturday when they make the trip to old rivals Bath.