"Sic (Simoncelli) for me was like a youngest brother. So strong on the track and so sweet in normal life. I will miss him a lot," Rossi wrote.
Davide Brivio, his manager at former team Yamaha, denied widespread internet and media rumors that the 32-year-old was too upset to carry on racing.
"Many are asking about Vale stopping races. This is absolutely not true and I'm sorry even that I have to explain it," Brivio wrote on Twitter.
Tributes have continued to pour in for Simoncelli from the motorsport community with his death coming only a week after British IndyCar driver Dan Wheldon lost his life in a 15-car crash in Las Vegas.
MotoGP bosses have started an investigation into Simoncelli's accident but have said it is too soon to comment on the fact his helmet came off.
(Writing by Mark Meadows, editing by Justin Palmer)