It was Juventus's second consecutive defeat since sealing a ninth Serie A title in a row, just days before their Champions League campaign resumes against Lyon.
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PSG said medical imaging had confirmed the initial test results of a sprained right ankle, with Kylian Mbappe also sustaining ligament damage.
Kylian Mbappe hobbled off in the first half of the French Cup final after a dreadful tackle by Saint-Etienne captain Loic Perrin.
Inter Milan pulled back ahead of Atalanta, and within four points of leaders Juventus, who are poised to claim a 36th 'Scudetto' when they play Sampdoria.
A tearful Kylian Mbappe was replaced but the greater concern for PSG will be the severity of his injury ahead of next month's Champions League quarter-final.
Atalanta moved level on points with second-placed Inter Milan, but are six points adrift of Serie A leaders Juventus.
Atalanta have now scored 93 league goals after their 6-2 win over local rivals Brescia.
Inter Milan moved above Atalanta and Lazio to go eight points behind league leaders Juventus.
Gervinho gave Parma a first-half lead but Inter Milan fought back with headers from Stefan de Vrij and Bastoni to snatch a vital win.
Italian Health Minister Roberto Speranza gave the green light to a "soft" quarantine, meaning that if a positive case is discovered only the infected person will be isolated.
Maurizio Sarri's Juventus fell in the Italian Cup final to Napoli on penalties midweek, having also lost the Italian SuperCup to Lazio in December.
Valencia said the coronavirus spread among the squad following last month's trip to Milan, "an area confirmed as 'high risk' by the Italian authorities days afterwards".
Josip Ilicic scored four times in a 4-3 win over Valencia that sent Atalanta into the quarter-finals 8-4 on aggregate.
Goals from Hans Hateboer, Josip Ilicic and Remo Freuler handed Atlanta a historic 4-1 win over Valencia as they closed in on the Champions League quarter-finals.
Josip Ilicic hit a hat-trick, including an incredible strike from the halfway line, as Atalanta crushed Torino 7-0 in Serie A.
Italian newcomers Atalanta will look to avoid another huge defeat at the hands of Champions League rivals Manchester City in Milan.
Atalanta secures their first ever UEFA Champions League spot with Inter Milan joining them. However, AC Milan finished fifth despite winning their final game of the season.