Omeruo played a key role in the Madrid side easing away from relegation in La Liga, and Leganes have long been interested in signing the defender on a permanent basis.
However, they have struggled to reach Chelsea’s demands to pay €7m and that has opened the door for other clubs in Spain, such as Celta.
Leganes still remain hopeful of doing a deal, despite the interest from Celta, and are continuing talks to try to reduce the demands for Omeruo, who can play at centre-back and right-back.
Omeruo has made it clear publicly that he is keen to leave Chelsea this summer despite Frank Lampard’s appointment as manager and his willingness to offer first-team chances to the club’s various loanees due to the FIFA-imposed two-window transfer ban on the Blues.
“I think now’s the time for me to leave, to find a place, to be my own man,” he said, with Nigeria through to the knockout stages of the Africa Cup of Nations, where they will face Cameroon in the last 16. “I’m married with a baby now, so I need stability.
"Chelsea have done amazingly for me, and for my family as well, but it’s the time when I need to reach my potential and get where I think I deserve to be.”
His journey away from Chelsea’s loan group would see him follow the likes of Tomas Kalas, who has signed for Bristol City in an £8m ($10m) deal, Ola Aina, who has left for Torino in an £8.7m ($11m) agreement, and Mario Pasalic, who has extended his Atalanta loan for €1m, with an option to buy at €15m (£13m/$16m), out of the door.