Ronaldo underwent surgery on his right ankle last Monday.
"We are going to use everything that is possible to us and that will help him recover as quickly as possible," Gaspar told Spanish sports daily AS.
"But Cristiano Ronaldo will not be in an optimum state for the competition until 12 weeks are up. He is working very well and he is optimistic.
"These first four weeks he will do the rehabilitation work in my clinic. After the first month, the Manchester United doctors will carry out another exam."
Gaspar added: "I want it to be made very clear that I am only involved with Ronaldo's recuperation and that I am in permanent contact with the medical department at Manchester United, with the Dutchman Niek van Dijk [the specialist who performed the operation] and with [Portugal team doctor] Henrique Jones.
"Any other information or the medical aspect about his injury are only and exclusively the concerns of Manchester United."