Vicente del Bosque says he keeps calling up Diego Costa to the Spain squad due to his qualities as a player, while admitting that the Chelsea striker could "soften" his character.
Costa, 27, has scored just once -- against Luxembourg -- in nine Spain appearances and has barely played for the nation over the last 12 months amid a series of injury problems, while Del Bosque said earlier this season that the attacker's on-pitch behaviour has been an issue in his thinking.
The Brazil-born player is, however, expected to start in Friday evening's friendly against England in Alicante.
Asked at his pregame news conference if he felt an "obligation" to keep picking Costa after persuading him to switch allegiances from Brazil, Del Bosque said despite recent issues the player remained a "useful" option for Spain.
"[Costa] is not with us due to any imposition, or any moral obligation we feel we have," Del Bosque said. "We know his character, and it is obvious he needs to soften in some aspects. He is here because we are sure that he can be useful. We trust in him. There is nothing agreed in advance."
On criticism Costa has received for not being at his best for Chelsea so far this season, Del Bosque said the real issue was that Jose Mourinho's side were struggling in general.
"When a team is not working properly, the players are also blamed," he said. "This year Chelsea are not going well, and this is happening."
Del Bosque also has Juventus' Alvaro Morata and Valencia's Paco Alcacer as centre-forward options in his squad.
He said he had not yet decided which XI would face England, with another friendly in Belgium also coming up on Tuesday.
"They all looked good to me during training these days," Del Bosque said. "They are always happy to come with the national team. We can play with one striker or two. We have an idea about the team. We will wait until after training [today] before making a decision."
Also speaking at the prematch news conference was Atletico Madrid midfielder Koke, who said that his former teammate Costa would come good in the end.
"There is a lot of pressure on Diego Costa," Koke said. "He is very happy to come with the national team. He wants to show what he did with Atletico, with Spain. We must have patience with him. I am sure that he will bring us lots of success."