The former Borussia Dortmund striker has scored in all three pre-season friendlies in which he has featured, including a brace helping Bayern reclaim the Telekom Cup with a 3-0 win over Wolfsburg on Sunday.
Ribery said he had been impressed by how Lewandowski had settled with the Bundesliga champions.
"It's always good for strikers when they strike," the France international said.
"He's new at Bayern and you know at Bayern Munich it's not easy in the first weeks.
"But until now he's really great and I hope he will be great in the future too."
Alaba said the Polish striker had already showcased to team-mates what he was capable of.
"We have a lot of fun with Robert," Alaba said.
"He shows every day in training what he can do and in these two games here I think everybody saw it."
Lewandowski's brace and a Sebastian Rode goal set up Bayern's win in the final of the pre-season tournament.
Ribery praised his team and particularly their ability to make the most of their chances.
"It is very important, the coach [Pep Guardiola] wanted us to attack very early and we did that well, made a lot of pressure on the opponents," Ribery said.
"We didn't have many chances in the first half but we converted very well, that's always good."
