Josip Ilicic returned to Atalanta on Monday after nearly two months away from the Serie A team for unspecified personal reasons, Italian media reported.
Slovene Ilicic, 32, didn't finish the last Serie A campaign following its post-lockdown restart, and returned to his home country in July.
The forward, a key player in a team that scored nearly 100 goals in Serie A last season, also missed his team's Champions League quarter-final with Paris Saint-Germain, lost 2-1 thanks to two last-gasp goals from the French champions.
His last appearance for Atalanta, who finished third and will feature in Europe's top club competition again this season, was the 2-2 draw at Juventus on July 11.
Italian media report that Ilicic was greeted by a group of supportive Atalanta fans outside the club's Zingonia training ground brandishing banners, including one depicting him with the match ball after scoring four goals at Valencia when Atalanta advanced to the Champions League last eight.
Contacted by AFP, Atalanta, who have been tight-lipped about Ilicic's reasons for going to Slovenia, refused to comment on the player's return.
Coach Gian Piero Gasperini has hinted that he will not be immediately returning to training, and he was not on the list of players called in to start pre-season sessions.
Atalanta also reinforced their forward line recently with the signing of Russia international Aleksei Miranchuk, who will likely fill the gap left by Ilicic in the early stages of the coming 2020/21 Serie A season.
Gasperini's side will start a week late after their opening match at Lazio was postponed to allow them a longer break following their European exertions.
Their first match will be at Torino on September 26 in the second round of fixtures.