Everton are still waiting to learn the full extent of England midfielder Ross Barkley's knee ligament injury.
It is feared the 20-year-old could be out for months after suffering damage to the medial ligament in training last week.
Barkley has responded well to initial treatment but swelling around the knee has so far prevented an accurate prognosis.
Martinez told the club's website: "I don't know where the figure of five months came from but obviously the extent of the injury is a little unsure at the moment because we don't know how the next two weeks are going to develop.
"It's a medial ligament injury and we know that Ross, in terms of the power and the strength that he has in his body, he could easily react to treatment a lot better than other players.
"The length that Ross will be out is a little uncertain at the moment and it could be anything between the eight weeks that we mentioned or a little further.
"Until the end of the week, or probably the next 10 days, we won't know how the knee is progressing and how quickly Ross can be back."
Barkley has battled back from a badly broken leg at the age of 16 to establish himself as a fixture in the Everton side and earn international recognition.
After loans at Sheffield Wednesday and Leeds, his big breakthrough came last season as he scored six goals and made 34 league appearances.
He was a member of England's squad at the World Cup in Brazil and, after reports linking him with a move, he signed a new four-year contract at Goodison Park last month.
He will have another scan in the near future as Everton continue to monitor his progress.
Martinez said: "Obviously we are keeping an eye, very closely, on how that knee reacts and every time we have a real improvement we are checking that.
"At the moment his knee is in a brace and this is a very important period of rehabilitation, making sure that the ligament can be repaired in a good position."