"When racing is that close, and this is the great thing about MotoGP racing, is that there is going to be passing and unfortunately the bikes will touch," Mamola told eurosport.com.
"Rossi admitted that it was a strong pass, and had he gone into that corner without Gibernau being there then he would have ran wide," he predicts, "but Rossi is not a rider who's going to just sit there and sit on his laurels if he's given a chance.
"People are saying that Gibernau left the door open, but let's just say that the door was closed but it wasn't latched," he added. "There wasn't a lot of room there and it was obvious that there was going to be a collision."
Mamola was also left disappointed by Rossi's provocative victory celebrations, whereby he shook Gibernau's hand with little interest before smirking to the Spanish crowd that were at that time chanting obscenities towards the Italian.
"For me, Valentino's reaction on the podium was a little bit too much," Mamola said. "There's a line between sportsmanlike conduct and rubbing it in people's faces, but that's Rossi. He's a multiple world champion but his reactions are very open away from the race track.
"He was very smirky-like, and you very rarely see that coming from a sportsman and I hope that it doesn't degenerate into a childish behavior," he added. "I've read that a sticker is going to be put on Rossi's bike that reads: 'How's my driving?' and that's just bad taste and rubbing it in."
Mamola, a two-time runner-up in the premiere class, was surprised to see how easily Gibernau had accepted Rossi's gestures, saying that the Spaniard must begin to believe that he can beat the Italian if he is to win the world championship.
"Gibernau has definitely made improvements since last season but Rossi is still rattling him," he said. "I'm a little apprehensive to say it fully, and the reason why I'm saying it is that Sete becomes reclusive, almost allowing Rossi to dictate."
