The Belgian has missed three out of United's last five matches due to injury.
"I watched Belgium play Brazil in the quarter-finals and it was clear that Romelu [Lukaku] and Eden [Hazard] were giving their absolute all," Cascarino said. "I don't think I've ever seen Hazard work so hard in a game.
"Fast-forward to the start of the season and he was eased into the Chelsea line-up by Maurizio Sarri, playing 14 minutes in their first game against Huddersfield Town and then 29 minutes against Arsenal.
"Sarri realised that Hazard needed a rest so he took him out of the firing line. The same cannot be said for Jose [Mourinho's] management of Lukaku.
"Someone has to step in and protect players when they are with their clubs, the manager or the medical team."