The Senegalese football federation (FSF) said 23-year-old Sarr "had taken an Air France flight from London at 11.30am and will arrive in Dakar in the evening".
Sarr's participation in the tournament that kicks off in Cameroon on Sunday had been in doubt after the FSF claimed Watford were blocking his release.
The FSF claimed last week Watford had displayed "disrespectful, pernicious and discriminatory behaviour".
Watford believe Sarr, who has not featured in a Premier League match since November and was not even named among the substitutes in their last two games, is not fit enough to feature at the AFCON.
Senegal's other Premier League stars, Sadio Mane of Liverpool and Chelsea goalkeeper Edouard Mendy, joined up with the squad at their training base outside the capital Dakar on Monday.
Senegal, runners-up in 2019, are one of the favourites for the African title.
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