The Colombian spent two seasons with Atletico, scoring 70 times in 91 matches before moving to Monaco last summer.
However, the 28-year-old has revealed that he is "not surprised" by Atletico's progress this season.
"Maybe I didn't expect them to be this strong and so in control. Yes we knew the team, in its third year with Diego Simeone, would be stronger," he told reporters.
"But for them to fight him on level terms with Real Madrid and Barcelona, who have a vastly bigger budget, I don't think anyone thought this was possible.
"What they are doing is admirable under Simeone, but I'm not surprised. I knew they had the potential."
Falcao is currently recovering from a serious knee injury.