The 2007 world champion, who had returned to the sport with the Enstone team after a rallying sabbatical, switched to Ferrari for 2014 following a Lotus pay dispute.
But while Raikkonen was highly competitive at the wheel of his black and gold car, the 34-year-old has struggled notably for pace now that he is back in red.
Asked if Raikkonen's 2014 struggle has surprised him, Lotus team owner Gerard Lopez admitted: "Yes, definitely.
"With us he was a strong rider, so the gap is a bit surprising," he told Germany's Auto Motor und Sport.
"But I also know how good Fernando (Alonso) is -- just imagine if he had had a Red Bull to himself for the past few years.
"But we also know how good Kimi is," Lopez continued. "It is a new team for him, and with Kimi a lot depends on what is happening around him.
"With us he was always fully comfortable, even though of course I cannot exactly know why things are not going right for him."