Diego Costa has returned to Chelsea for an assessment by the club's medical staff after withdrawing from Spain duty because of injury, a club source has confirmed to ESPN FC.
The 28-year-old, who sits top of the Premier League scoring charts with nine goals in 11 appearances this season, sat out Spain training on Tuesday and Wednesday as a result of the problem, which the source said is affecting his groin.
The Spanish Football Federation later announced that Costa had been forced to withdraw from Julen Lopetegui's squad to play Macedonia in a World Cup qualifier on Saturday and Tuesday's friendly against England at Wembley, with former Liverpool striker Iago Aspas drafted in as his replacement.
A Chelsea source said Costa has now returned to London and will be monitored and treated by the club's medical staff over the international break, with coach Antonio Conte hoping that his striker recovers in time to face Middlesbrough at the Riverside Stadium on Nov. 20.
If Costa is not fit to play, summer signing Michy Batshuayi is in line to make his first Premier League start since arriving in a £33 million deal from Marseille. Academy graduates Ruben Loftus-Cheek and Dominic Solanke will also provide alternative options.
Chelsea are second in the table after a run of five consecutive victories that has seen them score 16 goals and concede none since Conte's decision to switch to a 3-4-3 formation.
The Italian has picked an unchanged starting XI in his last four Premier League matches, with Costa finding the net three times.