Spain coach Vicente del Bosque has admitted that Fernando Llorente's lack of first-team action for Juventus is a concern.
Llorente has been restricted to a single start since joining the Serie A champions during the close-season, scoring once in five appearances against Chievo.
Del Bosque has conceded that the exodus of top Spanish players means competition for places is higher than ever, leading to contenders for a World Cup spot facing uncertainty over regular playing time.
He told reporters at an event in Las Palmas: "I worry about all those who do not play regularly.
"We are experiencing a phenomenon where a lot of our players are moving abroad," continued the 62-year-old.
"It is not harmful, it enriches us, but there are players in great teams that face a lot of competition for places."
The 28-year-old has scored seven times in 22 appearances for La Roja, but is without a goal at international level since 2010.
Liam Power
