The former Real Madrid man played an hour of Tottenham's 1-0 win against AC Milan last Tuesday after picking up the injury in the club's 2-1 win at Bolton on February 5.
Redknapp confirmed that his star forward suffered a recurrence of the problem in training on Sunday. But the Spurs boss is confident that the Dutchman will be back to full fitness for Tottenham's game at Wolves on March 6 and the club's crucial Champions League clash with AC Milan three days later.
Redknapp said: "Rafa did his calf again in training so he's struggling (for Tuesday's game against Blackpool).
"He missed a couple of games, played in Milan, got through 70 minutes and then didn't feel good on Sunday morning.
"It's a blow, he is a fantastic player. We need him but we can't get that run out of him.
"I'm hoping he will be back for Wolves. He should be okay, it's not a tear."
Tottenham's hopes of pushing for a top-four finish have been hampered by injuries to key players. Gareth Bale missed the win at the San Siro with a back injury and is not available for Tuesday's game against Ian Holloway's side.
Redknapp is hopeful that the Welshman will be fit for the second leg, though.
"Gareth is slowly improving and hopefully he's on his way back," he said. "He won't play against Blackpool but shouldn't be out for too long."
Source: PA
Source: PA