Postecoglou was speaking ahead of their Carabao Cup semifinal first-leg against Salah and Liverpool tonight in London.
"Mo is a world-class player, but if you put him in our team now I'm not sure he'll have that same level of performance because of the situation we're in as a group," said the Spurs boss.
"His attacking play, who do you need? You need a team that's kind of in good form, creating opportunities, playing on the front foot, having a really solid foundation of a defence that is cohesive. None of these things exist at the moment."
On comparisons with Spurs captain Heung-min Son, Postecoglou also said: "You've always got to give context. He (Salah) is playing in a fantastic team that are flying at the moment.
"I'd hazard to say that if you put Son Heung-min in Liverpool's team, I reckon his goalscoring return would be decent. It's hard for our players at the moment, they're trying awfully hard to be the best they can be.
"But when we're at our best, I still think you'll see Sonny's return, in terms of his ability to score goals and be really effective for us. I don't think that's diminished at all."