Honda rider Marc Marquez's third consecutive race victory in last weekend's Indianapolis Grand Prix means he leads the championship by 21 points over his team-mate Dani Pedrosa and 35 over Lorenzo.
In the manufacturers' championship, Honda heads Yamaha by 22 points.
"We need a push now, some pieces maybe, some evolution to be more competitive," said Lorenzo. "Because now it's difficult to fight with them."
MotoGP now has two more races on consecutive weekends at Brno and Silverstone, leaving little opportunity for upgrades before Misano in mid-September.
Lorenzo said his only hope is that the fast corners of the next two tracks will suit Yamaha better than the sinuous Indianapolis layout, where he fell from leading the race to finishing third behind the Hondas.
"With the bike we have, maybe in Brno it's going to be the same," he said.
"Brno and Silverstone are normally more suitable tracks for us. So let's see what happens.
"You never know in racing, sometimes something happens that you didn't expect. But in normal [circumstances] we must be better in Brno and Silverstone."