Chelsea duo Mateo Kovacic and Ethan Ampadu were both substituted in Wales and Croatia's 1-1 stalemate on Sunday.
Tottenham's Ben Davies went through the back of Kovacic right on the stroke of half-time, with the midfielder not returning after the break.
Three minutes into the second half Bruno Petkovic clattered into Ampadu from behind, with Ampadu quickly being replaced by Joe Merrell.
Gareth Bale's goal cancelled out Nikola Vlasic's ninth minute opener, keeping Wales' hopes of qualification for Euro2020 alive.
