Harry Redknapp's side find themselves three points behind fourth-placed Newcastle United, and will be looking to get back to winning ways against relegation-threatened Rovers, following a run of just one win in nine.
Meanwhile, the Lancashire club find themselves second bottom, and three points from safety, and a win at White Hart Lane would give Steve Kean's side a chance of Premier League survival.
Nelsen, who joined Tottenham from Rovers on a free transfer in February, has admitted that the players were disheartened after their latest setback – a 1-0 loss against QPR – and has called on them to turn their fortunes around with a home win this weekend.
"The lads were down after QPR, but you have to go back to basics, get motivated and believe you can do the job," said the 34 year-old.
"You have to take care of your own back yard and that starts against Blackburn. We have to win that game and it's probably a must-win game for Blackburn as well."
The New Zealand captain, who spent seven years at Ewood Park, is expecting a tough test from Kean's men, in a match that is equally important to both sides.
"Blackburn will be really up for it in the position they are in as well. It will be difficult game, we have to be completed ready for it and up for it, and I know we will be," he continued.
Nelsen has also told his teammates to be wary of the threat that his old Blackburn colleagues posses.
"There are some really good players there. Junior Hoilett is a fantastic prospect and we all know about Yakubu, he scores goals wherever he goes.
"They have some dangerous players, certainly, but so have we and we have to look at this game as a potential three points for us."
Three points for Blackburn will lift them above Wigan and out of the relegation zone, should the Latics lose against Newcastle.
Meanwhile, a win for Redknapp's team will see his side keep the pressure on the Magpies as they look for a top-four finish in the Premier League.