The Denmark international joined Celta in the summer of 2016 and has made 135 appearances for the club, scoring 18 goals, but his future now appears likely to lie away from the club.
A report in La Voz de Galicia claims Copenhagen – who came runners-up in the Danish top flight this season behind champions Midtjylland – have agreed terms to sign the winger.
He is one of a number of players who has been told they are no longer part of Celta’s plans by boss Oscar Garcia, with David Juncá, David Costas, Jozabed Sánchez, Juan Hernández, Emre Mor and Uruguayan striker Gabriel “Toro” Fernández also set to depart this summer.
Sisto has fallen from prominence at Celta in recent times and made headlines for all the wrong reasons earlier this year, when he broke quarantine and returned to Scandinavia with his sister via a 3,000km car journey.
Born in Uganda to South Sudanese parents, Sisto moved to Denmark aged just two months and went on to prosper as a footballing talent within the nation.
The winger has won 21 caps for his nation but has not appeared for Denmark since 2018.