Red Bull and Sebastian Vettel are leading Lotus and Kimi Raikkonen in both the constructors' and drivers' world championships after the first four 'flyaway' races.
But it might be argued that the bulk of Ferrari's deficit is because of Fernando Alonso's crash in Malaysia and malfunctioning DRS rear wing flap in Bahrain.
Asked, however, if Red Bull expected Lotus' Raikkonen to be challenging so hard in 2013, Marko told Kleine Zeitung newspaper: "We've known for a long time that they will be maybe the toughest opponents.
"At the moment we fear Lotus more than we do Ferrari," he insisted.
Asked if he really thinks Lotus will be a tougher challenger than Ferrari all season, Marko answered: "At the moment it looks like it.
"But there's only been four races, and we know that things can change.
"Actually, what is making the Lotus so quick in the races is a mystery to us."
Marko would not comment on the speculation the Enstone based team has perfected an hydraulically-controlled form of legal 'active suspension'.
But Red Bull is keeping an eye on Lotus for another reason.
Finn Raikkonen, the 2007 world champion and former McLaren and Ferrari driver, has been strongly linked with the race seat currently occupied by Mark Webber for 2014.
Asked if there is anything new to say on that topic, Marko insisted: "No.
"I've said it several times. We make our driver decisions before August, and that will be the case this year too."