Wolfsburg striker Grafite was rushed to hospital yesterday after a training ground accident.
The Brazil international, who has scored six goals in the Wolves' past three games, spent last night in the Wolfsburg clinic after colliding with Sascha Riether.
The pair reportedly went up for a header together, Grafite taking the full force of his team-mate's knee in the temple as they came down.
A statement on the Bundesliga club's official website read: "A exact diagnosis will probably follow during the course of Tuesday."
According to a report in the Wolfsburger Allgemeine Zeitung, Ricardo Costa stopped Grafite from swallowing his tongue as substitute keeper Andre Lenz and Marcel Schafer rushed straight to the changing rooms to summon physios Jorg Drill and Manfred Kross.
