Spurs suffered their second consecutive Premier League loss this season and their third straight north London derby defeat at home on Sunday.
Gabriel's second half header proved to be the difference, with the Brazilian leaping highest from Bukayo Saka's inswinging corner.
The defeat has left Tottenham 13th in the table and Redknapp insists they need to start picking up results sooner rather than later.
The former midfielder said speaking on Sky Sports: 'This time last year Spurs were fantastic to watch. We were all waxing lyrical about the manager and the free flowing football.
Jamie Redknapp has issued a warning to Ange Postecoglou after Tottenham's loss to Arsenal
'Right now it’s not free flowing. If you play well and don’t start winning then you get days like today where the quality drops.
'They need to pick up some results quickly. It’s a fact at this club if you’re not winning games you don’t get long and he needs to start winning some games.'
Former Spurs striker Les believes Postecoglou is the right man for the job, insisting the north London side are 'not far away'.
Asked whether he sees Spurs winning a trophy this season, Ferdinand responded: 'Not at the moment. First three games of the season they played really well.Today they were just missing that cutting edge.
'They’re not far away. I think he’s the right man for Tottenham at this moment in time and they’ll get it right. Today there was a lack of quality.
'In previous games there’s been a lack of personnel in the areas the ball has gone into. Solanke is going to take two or three games to get up to speed. I think Ange is the right man.'
Another trophyless season would stretch Spurs' silverware drought to 17 years but Postecoglou doubled down on his belief that the long wait will soon end.
The Australian struck a defiant tone in his response, but could barely conceal his irritation at the journalist's who asked whether he could win a trophy in his second season at Spurs.
'Yeah, absolutely,' Postecoglou responded. 'Am I going to answer the question or are you going to keep asking it?
'No, absolutely. I'll correct myself. I don't usually win things, I always win things in my second year.
'Nothing has changed. I don't say things unless I believe them.'