The Newcastle striker has flown home to Nigeria to be with his family, with no indication as to when he will return.
Martins' mother reportedly died of shock after trying to escape when a petrol tanker caught fire near her Lagos apartment.
"Oba was closer to our mother than anyone else in the family," said his brother Biola.
"He's still in shock and disbelief and feels terribly down. Oba always consulted her first in any decision to do with his career.
"Our mother stood by him when everyone else condemned his decision to dump school in pursuit of an unpredictable future in football."