Alcantara has not played a match for Liverpool since October 2020 after suffering a knee injury.
The European champions signed 23-year-old Roca to replace Thiago Alcantara, who has joined Liverpool, on a five-year contract in a transfer reportedly worth USD 10.5 million, plus bonuses.
The 29-year-old Alcantara, who joined the Premier League champions from Bayern Munich this month, will now self-isolate for at least 10 days as required by authorities.
The 29-year-old Thiago ended his seven-year spell at Bayern by moving for an initial fee of 20 million pounds ($26 million), with a potential additional 5 million pounds ($6.5 million) later.
Bayern head coach Hansi Flick admitted that the uncertainty makes planning "not quite so easy".
Thiago, who won seven Bundesliga titles with Bayern Munich is unlikely to sign a new deal when his current contract ends next season.
Battle of Borussias, return of Thiago Alcantara and three other things to watch out for in Bundesliga
In other news, star striker Mario Gomez is a doubt for Stuttgart ahead of their trip to Augsburg on Sunday.
Alcantara has left the national team camp due to a sprain in the internal ankle ligament which will prevent him from playing against Israel.
Bayern Munich received a timely boost on Tuesday when Thiago, Robben and Martinez all returned to training.