Rossi finished second behind Marc Marquez in the riders' standings this year after two wins and 13 podiums across the 18 races, but he still trailed the Spaniard by a whopping 67 points.
A slow start to the season, combined with Marquez winning the first 10 races, saw Rossi's title chances dwindle but he is convinced they can make a better start to 2015, if they work hard during the close season.
"We are really close to our rivals, but it will be difficult [to catch them]," he said. "[Jorge] Lorenzo will be stronger next year and Marquez won the world title by winning 13 races against my two.
"This means he won 11 more than me. The difference is huge.
"To fill this gap we have to work even better with the team, and also work hard with Yamaha to give us a hand.
"I think this year, especially at the beginning, Honda was much more competitive than our bike and the first half of the season was too easy for Marc.
"If we want to make life difficult for him, it's necessary to be closer to him."