Chelsea and Arsenal defenders Cesar Azpilicueta and Nacho Monreal are among the players being monitored by Athletic Bilbao, according to the club's president.
Athletic's transfer policy of only signing players native to or trained in Basque regions significantly shortens the list of potential targets the club can look at.
Among those on that list is Real Madrid midfielder Asier Illarramendi, whose days at the Santiago Bernabeu looked to be numbered following the January arrival of Brazilian starlet Lucas Silva.
But the club are also keeping tabs on the Premier League duo of Monreal and Azpilicueta, in addition to Atletico Madrid's Raul Garcia.
"There was interest from Athletic in players, although it was focused on Illarramendi," Athletic president Josu Urrutia was quoted as saying by AS.
"There are not so many players [we are looking at]: Illarramendi, Raul Garcia, Monreal, Azpilicueta.
"We have to be aware, monitoring – whether they continue at their clubs [or not], it is because they are interesting."
Monreal has struggled to hold down a consistent first team role at the Emirates since arriving from Malaga in January 2013. But a spate of injuries that ravaged Arsene Wenger's squad in the first half of the season saw the Spaniard take up a role at centre half in the absence of Laurent Koscielny.
But with those injury concerns easing and Gabriel Paulista arriving from Villarreal in the January transfer window, Monreal could see his chances dry up again.
Azpilicueta's position at Chelsea looks to be under no threat, however. After replacing Ashley Cole as the club's first choice at left-back last season, the 25-year-old is consistently preferred to summer signing Filipe Luis by Jose Mourinho in his first team.