The Spaniard had to come off midway through the second half with a thigh injury and early scans suggest Carvajal could be out for two to three weeks.
If true, it means head coach Zinedine Zidane will be without one of his starters for next Tuesday's home clash with Bayern.
'Los Blancos' will remain optimistic until the official prognosis on Friday but the injury does seem more serious than first thought given that doctors found a breakage of fibres in Carvajal's thighs.
However, if Madrid are to make it through to the final, their defender should be fit to play.
With Nacho also sidelined with a muscle tear, Zidane will be hoping for one of them to recover soon otherwise he will have to call upon youngsters Achraf Hakimi and Jesus Vallejo to fill the void, or use Lucas Vazquez as a make-shift full-back.