The Reds favourite has the distinction of being the fastest in the history of the club to reach the 50-goal mark, and is widely regarded as being among the best marksmen in the world.
The 26-year-old has been in and out of the treatment room for some time now, as he spent a portion of last season playing through pain to push his side further up the table - in a season that eventually turned out to be a gloomy one on Merseyside.
Torres has showed some recent signs he is returning to top form, scoring the only goal in the league win against West Bromwich Albion with a fantastic volley, and topping it with a strong performance for Spain by scoring twice against Liechtenstein.
But the recent goalless draw at St Andrew's saw the footballer turned television pundit launch a stinging attack on the forward.
Redknapp told Sky Sports: "Fans will suffer to a certain extent when you give the ball away, but they won't suffer a lack of effort.
"For 45 minutes he has been terrible. He hasn't got hold of the ball, he hasn't chased.
"He's been diabolical. I'm his biggest fan and I love seeing him.
"Of course you have to give the defenders credit but he's shown no appetite for the game. He has looked frustrated, sloppy and lethargic."
However, Reds boss Roy Hodgson rubbished comments made by the club's former player as he vehemently defended Torres.
He said: "I don't share that opinion, he is working hard for the team. As we saw towards the end, he's a constant thorn in the sides of defenders."
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