Villa, dubbed King David for his 51 goals in 82 internationals, fractured his left tibia in Barcelona's Club World Cup semi-final win over Al Sadd in Japan on December 15.
Del Bosque said he had spoken to Barcelona coach Pep Guardiola on Thursday for an update on 30-year-old Villa's recovery.
"I last spoke to his current coach yesterday. He told me how he is," the Spain coach told a news conference in Madrid, without giving details of the conversation.
"We have an obligation and also a conviction that we should wait until the last moment in David's case because he has been our most reputable goal scorer, the surest player and we should wait, of course."
In a separate news conference, Guardiola said of Villa: "His recovery is going very well. Better and better. Hopefully he will be able to go to the Euro."
Spain will publish a provisional list on May 15 including those going to the Euro and the London Olympics, he said.
Later, he said, the team will decide on possible players from Chelsea who face Bayern Munich on May 19, and then those from Barcelona or Athletic Bilbao who clash in the domestic King's Cup final May 25.
A definitive list will be drawn up May 27, Del Bosque said, but Spain could still wait to bring in Villa right up until May 29, the deadline for handing over the documentation to UEFA.
Del Bosque refused to say whether he would bring on Chelsea striker Fernando Torres, whose last-gasp equalizer against Barcelona on April 24 shattered the Catalans' hopes of reaching the Champions League final.
"We look at every day's play but we don't make a definitive decision based on one day," he said.
"We have to study the history of the players," the coach added.
"At the moment obviously I am not going to say whether Tom, Dick or Harry is coming to the team but we don't make a decision based on one single game."
Del Bosque said he respected Guardiola's "difficult" decision to end his four-year-reign as coach of Barcelona and take a rest, saying no one could have achieved so much in so short a period.
"I am happy and proud that we have Spanish coaches with the application and human values of Pep Guardiola," he said in a conference organized by Spain's Europa Press news agency.
"He has a good record on the sporting field and personally," Del Bosque added. "When we talk about Guardiola, it is a unique story -- you cannot compare it to anyone."
The Spain coach, who praised the level of Spanish club football as being among the best in Europe, repeated earlier statements that he was convinced that there was no doping in the game.
"I don't know if I am naive or innocent, but I don't believe there are people with such a lack of morals in football, I don't believe it," Del Bosque said.
"I believe in the values of the sport. If it were otherwise, it would be a disaster." (AFP)