Suarez believes the former Manchester United striker's game is good enough for the very elite level.
He told TMW: "Lautaro (Martinez) seems very interesting to me, while Lukaku is a player of strength and determination.
"For now he's okay but for tomorrow, especially if we want to reach increasingly important goals, we would need someone with more technical substance.
"For now he has done his part well but to point to other goals I would go to other players. At the individual level he works and helps the team but ... he stumbles too much on the ball."
Pressed that Inter coach Antonio Conte wanted Lukaku at all costs, Suarez added: "As my old team-mate Aristide Guarneri said, 'rather than nothing better something'.
"I don't think there was anything better on the market than Lukaku in the summer. And anyway I repeat, he is doing his part."