After Romain Grosjean was second fastest in both practice sessions on Thursday, Button's teammate Lewis Hamilton concurred that the "Lotus looks pretty good".
"Normally, there are seven tenths between the two tyre compounds," said the 2008 world champion. "Jenson was only four tenths ahead of Grosjean."
Button agreed: "Whenever they are going out, they are at the front. So I think that at the moment the Lotus is the car to beat," he is quoted by Germany's Auto Motor und Sport.
"That laptime of 1.16.1 is very quick on the hard tyre."
The Briton is quoted by Brazil's O Estado de S.Paulo newspaper: "It'll be tough to beat them."
In light of Lotus' apparent strength this weekend, Pirelli's Paul Hembery mocked those purists who think the constantly-changing race winners in 2012 are damaging the sport.
"(I'm) worried that Jenson said Lotus looking good in Monaco," he wrote on Twitter. "We risk a sixth winner in a different car.
"Disaster. Kimi and Romain, please do not win."