41-year-old Remko Pasveer sustained a groin injury during the first leg against Eintracht Frankfurt, leaving him sidelined for the upcoming weeks. Third goalkeeper Jay Gorter replaced Pasveer during the 2-1 loss.
UEFA rules state that a new goalkeeper can only be registered if two goalkeepers have sustained an injury for which recovery would take at least four weeks. However, the governing body of European football still granted Ajax permission to replace Pasveer with Matheus on the registration list.
32-year-old Matheus - who's in the top-10 of Europa League appearances with 58 - joined Ajax on loan in January after selling German goalkeeper Diant Ramaj to Borussia Dortmund. The Brazilian stopper has since started three games in Pasveer's absence and hasn't conceded a goal yet.
Eintracht Frankfurt-Ajax kicks off Thursday evening at 18.45 CET.