One player during the 90's who completely dropped off the radar was Igor Shalimov.
Probably
@Demyanenko_square_jaw knows better than me why. Going from Spartak under Romantsev to Foggia under Zeman where alongside Signori or Baiano they completely blitzed Serie A, then 2 years at Inter where he was more influential than Bergkamp or Jonk and won the UEFA Cup in 94.
After that season he was loaned to Duisburg don't know why and his performance levels completely dropped off. Not to mention when he was 30 his carrer at Napoli was over related with the famous nandrolone suspensions who were "frequent" on Serie A during the late 90's.
Shalimov was one of the biggest examples of the poor professionalism that developed in a lot of the late 80s and early '90s generation of ex-ussr players when they moved West. A lot of them did well initially then after a couple of seasons decided they preferred the lifestyle and partying over the amount of dedication needed to stay at a high level, Kulkov, Korneev, Mikhailichenko, Lediakhov, Yuran etc..
I remember Shalimov in interviews when he was doing really well at Inter moaning and complaining about the level he was expected to maintain week in and out, despite in his eyes having proved himself by playing a great six months or so and seeing off Matthias Sammer(they could have played together, but i guess he saw him as direct competition because off the strict foreigner rules) it wasn't that surprising that within a couple of years he had dialled back the effort and become more of an inconsistent mid-table player that would put in the occasional great performance against the bigger teams.
He also lead the player revolt of the National Team after the 94 world cup qualifiers which destroyed all unity in the squad for the final tournament and meant quite a few first team players like Kanchelskis didn't go.
Probably one of my least liked players ever, though i have to admit he was an excellent footballer when he could be bothered, very elegant, great vision, technically gifted, equally good with both feet and was developing into a good goalscorer too. 18 league goals alone in those first two Serie A seasons was impressive for a genuine midfielder. It was only beasts like Matthaus that were exceeding that in Italy at the time from midfield.
There's a short clip of some of his Inter goals with some great finishes.