The 24-year-old forward enjoyed a dream debut for his country  on Saturday, netting one goal and winning the penalty which allowed Santi Cazorla to seal a 2-0 victory against Serbia.

Del Bosque was full of praise for the Atletico striker, but said that he could not select players who are new to the national team set-up.

"We preferred other options, but we have to say that Adrian was brilliant," Del Bosque told reporters.

"The seven players who have been left out are a bit sad, but they are good sportsmen.

"It was unthinkable that a player who just had their debut would make the squad. But we are keeping an eye on him."

Valencia striker Roberto Soldado was also left out of the squad and Del Bosque gave the reasons for his omission.

"Alvaro Negredo and Soldado are two extraordinary players, but different," he said.

"One is quicker, but the other is more of a team player. David Villa is irreplaceable, because of his characteristics.

"We have to look for solutions, and we have them in every area of the field. But I have to say it: for all that Villa has given us, he cannot be replaced.

"The same thing can be said about Carles Puyol, whose absence is also a heavy blow for us."

Earlier in May, Del Bosque had hinted that Pedro could stay at home, but the Barcelona attacker has been included in the 23-man party for Poland and Ukraine.

"He had an irregular season, like many others did, but we tried to look at his path in the medium run," Del Bosque said.

"That is why we have called him up. We need people who can play out wide, who are effective and who can add quality to the bench."

There are only four changes to the list when compared to the squad which won the World Cup in South Africa, but Del Bosque insisted that this is not a veteran group.

"There is no reason to doubt these players," he added. "Not many players are aged over 30 and the rest are in their prime.

"Groups must be pumped with new blood, but we must not make changes without any reason."

Meanwhile, Barcelona have announced that Cesc Fabregas will spend up to 10 days on the sidelines with a muscular injury.

The 25-year-old midfielder came on as a late substitute in Barca's 3-0 victory against Athletic Bilbao on Friday, replacing Xavi with only 10 minutes left in the Copa del Rey final.

Fabregas will miss Spain's upcoming friendlies against South Korea and China.

Spain will kick off their Euro 2012 campaign against Italy on June 10 before meeting Republic of Ireland (June 14) and Croatia (June 18).