The Spurs full-back was reflecting on the north London side's disappointing defeat at Crystal Palace last weekend and knows both he and his team-mates must be on their guard to avoid a repeat at White Hart Lane this afternoon.
Sunderland's two individual threats in particular, according to Walker, are winger Johnson and former Tottenham striker Defoe.
The Black Cats announced the signature of the 32-year-old yesterday afternoon and he has been cleared to play against his former side.
Walker, meanwhile, believes his side can take no chances with either of the forwards.
"You’re always going to get a good, hard-working team [with Sunderland]. They’ve got some good players, as well," the Tottenham defender said during the interview.
"I’ve played with a few of them with England. Johnno (Johnson) is always a good threat and, I don’t know whether he can play or not (it has since been confirmed that he can) but we’ve seen countless times what Defoe can do in a Spurs shirt.
"As defenders, we’ll have to be on form with him."
Kick-off is at 3pm at White Hart Lane, as Sunderland look to improve on a record of just 18 goals in 21 Premier League games, while Tottenham look to close the gap between themselves and fourth-placed Manchester United - which currently stands at three points.