Joshua was shocked by underdog Ruiz Jr. last month and lost his IBF, WBA and WBO heavyweight championships and his immediate hopes of an undisputed title fight with WBC champion Wilder, Sky Sports reported.
"It is not over for Anthony. Just because you lose, it doesn't mean it's over," Wilder exclusively told Sky Sports.
"Even if he loses the rematch, which I feel he will.
"I don't think he knows how he lost. He was knocked down four times. He gave up, in my opinion."
Joshua is expected to go straight into a second fight against new champion Ruiz Jr. in an attempt to regain his world titles.
"I wasn't surprised," Wilder reflected on the first Joshua vs. Ruiz Jr. fight.
"I was happy for Andy, for where the guy came from. Like a lot of us fighters, he was looking for the lottery tickets.
"He said: 'Mama, we ain't got to struggle any more'.
"That touched me because we all come from some type of place. We are all trying to support our families. We are all looking for the meal ticket.
"To do that when everyone was against him is amazing.
"It was an upset for the champion but it is good for the sport."
Unbeaten Wilder is expected to rematch Luis Ortiz and Tyson Fury.
"The heavyweight division is so lit, it is so exciting," he said.
"I remember a time when it was in a dark place but it has found light. Everybody is talking about the heavyweight division.”