Chelsea are conducting their own tests on Alvaro Morata to determine how long the striker will be out for.
Morata was left stunned after the Spanish national team's medical department revealed on Monday that he has suffered a grade II myofascial injury in the hamstring.
The 24-year-old limped off against Manchester City on Saturday but he, along with coach Antonio Conte, was confident the problem wasn't too serious having been briefly examined after the match.
As Standard Sport revealed on Monday, Morata told friends before leaving Stamford Bridge that he expected to be sidelined for a only a few days and that he'd return to training in time to face Crystal Palace on October 14.
But that is now in doubt after he joined up with the Spain national team on Sunday and underwent an MRI scan on the problem.
It has been reported that the Spain international now faces being out of action for four-eight weeks, however Chelsea have not confirmed this is the case yet.
Losing Morata, who is the club's top scorer with seven goals, for any length of time will still be a major blow for Chelsea.
After the international break is over, they face six games in the space of just 17 days, including matches against Roma home and away in the Champions League.
The Blues didn't buy another centre forward in the summer and have only Michy Batshuayi, who has started just 11 games since joining from Marseille for £33.1m last year, as their other recognised striker.
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Conte could opt to play Eden Hazard as the frontman instead, but he struggled in the role after being moved there following Morata's departure in the 1-0 loss to Manchester City.