Ajax forward Leonardo is expected to be ruled out for the rest of the season after sustaining a knee injury in the 1-0 defeat to Heerenveen.
The Brazilian came on as a second half substitute but lasted just 16 minutes before colliding with Heerenveen defender Michel Breuer.
He will undergo scans on Monday but an early assessment from the Ajax medical staff suggests he has damaged his cruciate ligament.
"We have lost Leonardo for a very long time," declared coach Henk ten Cate.
"It is a cruciate ligament injury, although we can only tell with certainty after an MRI-scan."
Leonardo, who has had serious knee problems in the past, only joined Ajax from NAC Breda in January.