Chelsea suffered a 1-0 defeat at bottom-of-the-table Southampton in the Premier League on Saturday, heaping more pressure on manager Graham Potter.
Southampton’s James Ward-Prowse scored a free-kick just before half-time which proved enough to edge his relegation-threatened side to victory at Stamford Bridge.
Azpilicueta required nearly 10 minutes of treatment on the pitch after being hit on the head in a goalless struggle in the second half. Physios from both clubs rushed to his aid and the Spaniard was eventually carried off on a stretcher.
Chelsea came alive in the second half when Raheem Sterling and Kai Havertz came on and put the Southampton defense under pressure.
Southampton goalkeeper Gavin Bajunu was kept busy and produced a fingertip save from substitute Conor Gallagher in the dying seconds of extra time.
The result – leaving Chelsea with just one win in 10 games this calendar year – caps a poor week for the west London club which saw them lose late in the first leg to Borussia Dortmund. Their Champions League round of 16 tie ended.
Chelsea are 10th with 31 points from 23 matches, 10 points behind the top four.
Potter left Brighton in September to replace Thomas Tuchel, but has struggled to revive Chelsea’s fortunes despite spending heavily in the January transfer window.
Meanwhile, Southampton remain in last place but three points from safety and are under caretaker coach Ruben Seles after Nathan Jones was sacked a week ago.
“It’s been a difficult season for us,” Ward-Prowse told the BBC. “We are missing consistency in all aspects of our game. Ruben came in this week and was fantastic. He steadied the ship and calmed everyone down.”