Del Bosque said he would give Villa - Spain's all-time record scorer - every chance to be involved in Poland and Ukraine.
"We are hanging on every day but have no definitive answers," he said.
"We need to evaluate the fitness of the players. The last stretch of the season is important. We must see who will be the best for our game.
"We look at all scenarios regarding David Villa. Yesterday I spoke with his coach. We know the score. We are obliged to wait until the last moment for our frontman and proven goalscorer."