Mourinho's men are now seven points behind Wolves and Manchester United with six games to play.
"This might be the worst squad Mourinho has ever inherited," Cascarino wrote in The Times.
"When he took over at Spurs in November he said that he was taking on a team that contained players he had tried to sign. I'd really like to know who he was referring to, because none of them look worth splashing the cash on."
He added: "If I was coaching a side about to face Tottenham, I would immediately pounce on the full backs as an area of weakness and this is exactly what Wilder did.
"It gets worse. The centre-half partnership is a disaster zone. When Mourinho, as Manchester United manager, prepared to face Ajax in the final of the Europa League in 2017, he identified Davinson Sánchez as a weak link and yet he is now placing faith in that very same player."
As well as going on to label Eric Dier "slow and static", Cascarino said Kane is now "neglecting his overall contribution."