Seselj's medical team has expressed concern that the Hague tribunal has not referred him to undergo additional tests, media reports said.
Last week, Seselj's medical team sent to The Hague a list of tests that should be performed to rule out the possibility of a malignant disease.
Seselj appeared before tribunal judges on Tuesday for the first time since he ended a hunger strike in December last year.
The Hague tribunal indicted Seselj in 2003 for war crimes committed in Croatia and Bosnia in the 1990s and the ethnic cleansing of Croats in the northern Serbian province of Vojvodina.