Liverpool and Manchester United have reportedly posted scouts to run the rule over a number of players from La Liga outfit Rayo Vallecano.
According to Spanish newspaper AS, the north west rivals have also been joined by Sunderland, Fulham and Everton representatives at the Campo de fútbol de Vallecas in recent weeks.
The objects of desire for Liverpool and United are reported to be Rayo trio Michu, Lass and Jordi Figueras, all of whom have played starring roles this season.
After winning promotion from Segunda last term, Rayo are currently eighth in Spain's top-flight - above the likes of Atletico Madrid and Villarreal.
Jordi, 24, signed for Rayo in August from Valladolid and has been solid and composed at the back.
Meanwhile, 25-year-old Michu midfielder Michu has found the net on five occasions since signing from Celta Vigo, while teenager Lass has also been linked with Real Madrid.
Liverpool, meanwhile, retain a healthy relationship with Rayo after Dani Pacheco left Anfield on loan via Atletico.
This could see Kenny Dalglish move into pole position in pursuit of Michu, Lass and Jordi, although United are expected to contest Liverpool.
Sir Alex Ferguson's scouts in Madrid are also said to be monitoring Real's Angel di Maria as the United boss identifies targets to bring to Old Trafford in January.