Atletico Madrid defender Juanfran has sustained a hamstring injury, the LaLiga club have confirmed.
The experienced full-back was replaced by Thomas Partey after 36 minutes of Saturday's 1-0 home win over neighbours Rayo Vallecano.
An MRI scan has confirmed a muscular problem in Juanfran's left leg but Atleti are unsure over a timeframe for his return at this stage.
Juanfran regained his status as Atletico's first-choice at right-back following Sime Vrsaljko's move to Inter on an initial season-long loan deal.
Colombia defender Santiago Arias provides an alternative for head coach Diego Simeone, but is yet to make a LaLiga matchday squad since joining as Vrsaljko's replacement from PSV for €11million at the end of last month.