Redknapp believes the midfielder is being advised to do everything he can to engineer a move to Chelsea. Modric has been at the centre of a summer-long transfer tussle between Spurs and Chelsea, who have had two bids for the player turned down over the past two months.
Yesterday, it was reported Chelsea were ready to mount one last £40 million (Dh240m) bid for the playmaker before the transfer window closes on Wednesday night.
Modric missed last week's defeat to Manchester United because he was not "right in the head", according to Redknapp, but the 64 year old gave the Croatian the OK after he came through training without any problems this week.
Modric played 65 minutes, but only after Redknapp convinced him that he had to start.
Redknapp said: "Luka came to me at 11.30 this morning and said to me, 'I don't feel my head is right today'. I said, 'I feel you need to play today, Luka. I need you to play. You need to come and play'.
"I told him we had injuries and I said, 'I need you to come and play. We need you on the pitch, get out and play'. I told him he was our main man."
"I'm sure he is getting advised to maybe not play today. We have seen it with other clubs," Redknapp added.
Redknapp is still convinced that Modric will stay at the club, but concedes the whole saga, and transfer speculation over the future of his other players, has cast a dark cloud over the club's start to the season.
"There has been a feeling around the place that the place hasn't been right since the start of pre-season," Redknapp added.
"It has been a bit of a difficult period really. When people want to go it can be a problem, but hopefully in another day or two when the window closes he will still be here and we'll all move on.
"I don't think he's going to go. The chairman said he isn't. When he comes back from international duty the window will be closed."
The result will have done little to convince Modric that Spurs can offer him the same chances of success as is being offered at Chelsea.
Two years ago, the north London club beat City to fourth place and they ran them close for the majority of last season.
Yesterday, however, the gulf in class was clear. Nasri, who moved to City from Arsenal last week, supplied the crosses for Dzeko, a £27m January buy from Wolfsburg, to score his first two goals and he also played his part in the run-up to Aguero's strike, which made it 4-0.
Dzeko, who had clinched his hat-trick by firing in from six yards on 55 minutes, scored his fourth - a beautiful curling effort - with the last kick of the match. City have won all three of their Premier League matches, scoring 12 goals in the process.
Roberto Mancini, the manager, however, was quick to play down suggestions that such form means his side are certain title contenders, saying: "This is a very long season and it's important that we started well.
"The next games will be very hard because now everyone thinks we will score three or four goals, but that is impossible."
Another blow for Redknapp is that Rafael van der Vaart looks to be out for a few weeks at least having suffered a hamstring injury that resulted in his second-half withdrawal."Rafa tore a hamstring," Redknapp said.
One ray of light for Redknapp is the news that he is close to signing Scott Parker, the England midfielder, from West Ham United, while his Honduran midfielder, Wilson Palacios, was at Stoke City yesterday ahead of a move away from Spurs.