"They are good players, but far too many of them are under-performing and they have been for a while," he told Sky Sports. "This is Chelsea we are talking about now.
"Chelsea on a bad year should be top six. They should still be there or thereabouts, but where they are just above the relegation zone is impossible."
British bookmakers slashed the odds on Mourinho, who said he felt his work was "betrayed" by his players' performance at Leicester, being the next premier league manager to be dismissed to 8/11 on Tuesday.
The result left Chelsea in 16th place, just one point above the relegation zone after nine defeats in 16 league games, and 20 points adrift of leaders Leicester.
"I don't know whether he's lost them, but something has to change. It has to change right now -- whether it's attitude, or performance, or something else, it has to change," said Lampard, 37, who made 648 appearances for Chelsea and scored 211 goals.