After slumping to a 2-0 loss at home to Stoke City on Saturday, QPR are 10 points from safety with four English Premier League games remaining.
 
Redknapp has led several teams from the brink of relegation to safety but said his QPR side had little hope of staying in the top flight.
 
"It looks like that's it," Redknapp said. "It is almost impossible now.
 
"It is a big disappointment but even today I felt in the first half we were bang in the game. I was disappointed to come in at half-time 1-0 down as I thought we did OK in the first half.
 
"But we lack a forward ball and without Bobby Zamora it is very difficult. We've got no real target up there.
 
"Loic Remy needs to play off somebody as he is not a target man and it was just a problem for us."
 
If Aston Villa can cause an upset and beat Manchester United at Old Trafford on Monday, the fates of QPR and Reading will be decided.
 
Redknapp said he had given his all to try and keep QPR up but believes it simply has not been enough.
 
"It is disappointing but I've had other disappointments and I'll have more in the future I am sure," Redknapp said.
 
"I get as disappointed as anyone when it doesn't go well but you can only do what you can do.
 
"I can't look back and say I have not worked hard and tried hard because I have. I have given everything and at the end of the day it just hasn't been good enough."
 
Stoke City assistant manager Dave Kemp said his side needed to build on their win after they moved six points clear of the bottom three.
 
"We just have to keep going after that," he said.
 
"We've got four more games and we need to concentrate on our performance and getting more points.
 
"We're certainly not going to sit back and rest on that now. We've had a bad run and obviously came out of it today with the points so we've got to keep that going in the last four games."