Atsu has been locked in a contract wrangle with Porto all summer, with the club keen to tie down the Ghana international to a new deal and increase his buy-out clause.
However, the 21-year-old has refused all offers from the club as he seeks to win a move away from Porto.
Atsu was left out of Porto's pre-season tour of Holland and the club have now decided to sell the skilful winger.
Liverpool have been strongly linked with a move for Atsu, but Sky Sports understands Tottenham and Everton are now actively monitoring the player's situation at Estadio do Dragao.
Porto have decided to cash in on Atsu this summer rather than lose him on a free transfer in a year's time and the news has alerted the African's suitors.
"Porto have indicated they would be willing to sell Christian now as he will not sign a new deal," a source close to the player told Sky Sports.
"Christian has always said he would like to play in the Premier League and a number of clubs are interested in him."