Rossi's comments came after Marquez dominated in the second round of testing at Sepang, Malaysia. The Italian seven-time world champion believes Marquez will continue to lead the field.
Rossi was quoted by crash.net: "For me Marquez is the more competitive. He was faster on the time attack but also in the race simulation and I think Marquez and Honda are the favourites to win the championship.
"But it depends very much on the track. And you know the test is not a race weekend. It is completely different. You work in another way. Always start-stop. The race is another thing. But I think more or less the gap remains the same."
Rossi added: "In general I'm happy about the test because our main issue is to understand the gearbox, which is good. I like it and it can help us a little bit. I'm not very happy about my time attack today because for me I have a better potential.
"I have the potential to stay in the top three, but I always take traffic. One time Pedrosa, one time Bradley Smith – but it is my mistake. The rider has to decide the moment to have the clear lap. Anyway the test position is not very important, it is just for fun!
"I think it will be very interesting and I'm very curious to understand our potential at another track like Qatar. To understand the difference between Honda, Ducati and Yamaha."