The Bundesliga side, who are competing for a place in Europe, have seen their form dip as they have struggled with injuries in recent months.

They have lost their last three matches in the domestic league, and just edged past second-tier club Arminia Bielefeld earlier this week in the DFB Pokal.

Frankfurt were without nine injured players in that match, and looking ahead to their league game against Freiburg this weekend, Kovac said that he hopes at least defender Bastian Oczipka can return to the squad, if need be also with the help of painkillers.

"You can't do without painkillers in football," the former Croatia international said. "Those who think that there is professional football without the use of painkillers are on the wrong track. The pros stretch their bodies to the limit."

Oczipka sustained an ankle injury while in training earlier this week, but could be employed in central defence with Real Madrid loanee Jesus Vallejo sidelined with a muscle injury and David Abraham suspended.