Udinese's Maurizio Domizzi is a major doubt to face Arsenal in the Champions League preliminary round.
The veteran defender had recovered from a muscular injury on July 30 during a friendly against Nice.
However, he pulled up again in Saturday's training session with a left thigh problem and club medics are increasingly concerned.
It looks unlikely that Domizzi will be able to recover in time for Tuesday's trip to the Emirates Stadium in London.
It would be a heavy blow for the Friulani, whose defence is already a work in progress after Cristian Zapata was sold to Villarreal this summer.
Arsenal started their Premier League season on Saturday with a 0-0 draw away to Newcastle United. New buy Gervinho was sent off for slapping Joey Barton.