The 2007 season was dominated by Ducati's Casey Stoner, who took ten victories on his way to his first MotoGP title.
The Australian, however, is currently fourth in the standings and it seems Ducati's rivals have closed the gap to the Italian squad.
And Yamaha rider Rossi, third in the championship, believes more teams will be joining the fight in front.
"It looks like this year the situation is more balanced," Rossi told a news conference. "Now I'm third in the championship, ten points behind the leader. There are a lot of great riders.
"We are four (riders) in front in the championship but I expect also some good bikes from the second group to catch us."
Rossi is looking to end his victory drought this weekend, not having won in six races, his longest win-less streak in MotoGP.
The Italian has always finished on the podium at Estoril in the top category.
"I like this track," he said. "It's an old style track. We come from a good result at Jerez.
"I was not very worried after Qatar because I knew we have good potential and even if I didn't win in Jerez it was a good result," added Rossi, who finished in fifth in Qatar.autosport.com