Spain coach Vicente del Bosque has insisted bad-boy striker Diego Costa is no criminal despite admitting the Chelsea striker has a penchant for "unsavoury incidents."

Costa's repeated selection has been controversial ever since he was convinced by Del Bosque to turn his back on the country of his birth Brazil to play for Spain at the 2014 World Cup.

Spain's defence of their world title was subsequently disastrous as they bowed out after just two group games after thrashings by the Netherlands and Chile.

Meanwhile, Costa's individual displays at international level have done little to justify his place since as he has scored just once in 10 appearances -- in a 4-0 rout of Luxembourg 19 months ago.

Costa's fiery temperament has also come under even greater scrutiny during a difficult second season at Chelsea.

Yet, Del Bosque insisted if Costa is left out of his squad for Euro 2016 on May 17, it will be due to his form and not a fear that he could cost his side by losing his cool in France this summer.

"We can justify if he has played well or badly, but he has committed no crime," Del Bosque said in an interview with news agencies, including AFP.

"With us he has always acted correctly. There have been some unsavoury incidents, but he hasn't committed any crime and he always comes here with plenty of desire.

"That is what we value and we are not going to doubt him because of his behaviour."

La Roja are looking to bounce back from their World Cup disappointment in style by winning a third consecutive European Championships in what is likely to be Del Bosque's last stand after four major international tournaments in charge.

The former Real Madrid coach has been criticised in the past for being too loyal to some of Spain's golden generation whose glory days are now behind them.

The debate between whether 166-cap captain Iker Casillas or Manchester United's more in-form David de Gea should start in goal being the most glaring example.

However, Del Bosque insisted he will pick a side with enough youthful enthusiasm to mount a serious challenge to retain their title.

"I believe a lot in the veterans that have spent a lot of time with us and the new ones that are coming to give us the boost of fresh blood that they offer," he added.

"Our objective is not to think that we have won two consecutive European Championships because people aren't going to value that, but what we do in this Euros.

"We have the dream and the objective to have a good tournament, but we are not so arrogant to think we will turn up and win it.

"Having won two in a row shows we have a strong team, but nothing more. We need to show it out on the field."

Worryingly for Del Bosque, some of the circumstances preceding their flop in Brazil two years ago have been repeated this season.

Real Madrid and Atletico Madrid will once again contest the Champions League final just 15 days before Spain's opening match against Croatia, whilst the two Madrid clubs are also involved in a tight three-way battle for the La Liga title with Barcelona.

But Del Bosque believes getting some of his players mentally right after the disappointment of missing out on the Champions League and La Liga is as important as being physically fresh.

"There are always concerns because the seasons are very intense at club level and, as we have seen, the players get to the end of the season very tired," he continued.

"Defeats at the end of the season can have an effect. The optimism of winning can help when the players come to the national team, but not everyone can win.

"We will see if we are capable of managing it so that we start the competition not just in good condition physically, but mentally too."