The Gunners were left depleted early in the season after Fabregas completed his long-awaited move back to Barcelona in the summer while Nasri moved to Manchester City.
But despite a poor start to the season, they are now fourth in the Barclays Premier League table.
And Walcott reckons the departures of the two players have galvanized the squad.
"I'm not saying that Cesc and Samir were individual players, they were great team players, but when you lose two top players everyone needs to come together," Walcott told Arsenal Player.
"The manager has brought in some good additions and we are a bit more of a team, we work harder when we haven't got the ball.
"We have a lot more clean sheets as well, and having [Thomas] Vermaelen back is very important as he is a massive player for us."
While hailing his side's strengths, Walcott admitted the players need to share the burden of scoring with Robin van Persie.
"The next thing the whole team needs to share the goals more," Walcott admitted.
"Samir and Cesc used to get quite a lot of them and Robin van Persie has been getting most of them so that's our next step."
Arsenal take on Leeds in the third round of the FA Cup on Monday.