It came after Pompey finally landed Kanu, who was set to sign the new deal thrashed out to keep him at Fratton Park.
The Blues had sounded out Boro about bringing Yakubu back to Fratton Park.
Predicted Portsmouth XI v Cheltenham: changes expected to side that beat Cardiff so handsomely - but attacking duo could keep places and defender set to return
Portsmouth transfer news: Blues youngsters attracting interest but Danny Cowley has no desire to cash in just yet
Portsmouth boss Danny Cowley makes transfer admission as former Luton and Millwall midfielder edges closer to Fratton Park exit
Former Portsmouth keeper Alex Bass suffers tough night on and off the pitch as he makes Sunderland debut following Fratton Park exit
League One latest: Oxford land former Pompey striker target from Swansea as Sheffield Wednesday bemoan exciting duo's move to Brentford and former Peterborough boss criticises club
Redknapp remained keen to add another striker to his ranks, despite ending the protracted saga over Kanu’s future.
The Pompey boss believed he was still a player light up front after deciding to use John Utaka mainly as a wide man for the season ahead.
The Blues had been in touch with their rivals in the north east and deals involving players as well as cash had been mentioned.
Then Middlesbrough boss Gareth Southgate wanted Gary O’Neil.
But, despite reports, Southgate wasn't so keen on taking Sean Davis to the Riverside.
Speaking to The News, Yakubu’s agent, Barry Silkman, claimed Pompey would not have the cash to buy the then 24-year-old after already spending £23m that summer.
Silkman said: ‘Yakubu will not come cheap. I honestly believe Pompey don’t have the money to pay for him.
‘They have spent a lot already. I don’t think they have got it left.
‘I know Harry loves Yakubu. He’s desperate for a goalscorer, and, after Thierry Henry, Yakubu’s got the best goal ratio in the Premier League.
‘Portsmouth haven’t made a concrete bid for Yakubu, but I would say they have made more than an inquiry.
‘The problem is, the season is not far away and it costs a lot of money to replace a player like Yakubu.
‘Maybe Portsmouth thought the price would go down the closer it got to the season.
‘But Middlesbrough will look at the money Portsmouth have spent for David Nugent, Sulley Muntari and John Utaka and think Yakubu is worth more. That’s where the problem begins.
‘He is proven to score a goal every two games in the Premier League. Players like that are hard to find.’
Of course, Yakubu didn’t return to Pompey in that summer of 2007.
Instead, the Nigerian international moved to Everton for a fee of £11.25m on a five-year contract.
At Goodison he established himself as a fans’ favourite, scoring 25 goals in 82 appearances.
The striker also enjoyed successful spells at Leicester and Blackburn before hanging up his boots in 2017 following a spell at Coventry.
In total, Yakubu scored 43 goals in 92 Pompey appearances following his initial loan move from Maccabi Haifa in January 2003.