Couple of older signings have stuck with me who were absolutely disastrous. In 1990 when Juventus were buying Roberto Baggio and Milan were signing, well, everyone, Inter's big attacking signing was.... Davide Fontolan from Genoa. He cost £5m which surprised me a lot considering I followed Italian football closely and was barely aware of the name.
He was a wide attacker, left-sided I think. He was quick enough but not really a scorer with a 1 in 4.5 goal record at Genoa. Then early in his Inter career he did his knee badly and when he came back I'd like to say he was never the same player, but I had seen so little of note from him in the first place to know what his benchmark was. Somehow he hung around for 6 seasons and left Inter with the total of 11 goals.
In 1993 they expensively signed Franceso Dell'Anno from Udinese. He was quite an elegant footballer, a real number ten but never quick enough in movement or thought to do what the likes of Baggio or Orlando or Zola could do in that role. Also he arrived at the same time as Dennis Bergkamp who was one of the best hybrid 9/10s in the world, but of course Inter saw as exclusively a 9. Dell'Anno was meant to be the one who supplied the Dutchman, but they got in each other's way and Dell'Anno never looked like he had the personality to play at that level.