Fabio Borini's £14m move from Liverpool to Sunderland is yet to be completed.
The clubs have agreed a fee but the striker still needs to agree personal terms and will play for Liverpool in the friendly with AS Roma on Wednesday.
Black Cats boss Gus Poyet said they needed to "get in touch with the player and start negotiating", while Reds boss Brendan Rodgers said Borini is "considering" the possible move.
Borini, 23, spent last season on loan at Sunderland and helped them stay up.
Sunderland manager Poyet is keen to push the deal through but admitted: "The agreement was with the club, not with the player.
"You never know how long [negotiations with the player] will take."
Italy international Borini scored 10 goals during his stint at the Stadium of Light and picked up the club's young player of the year award as they avoided relegation from the Premier League.
Borini was Rodgers' first signing as Liverpool boss and moved to Anfield from Roma for about £11m in July 2012.
However, the forward struggled to make an impact on Merseyside, scoring just two goals in the 2012-13 campaign before his loan move to Sunderland.
His first goal for Poyet's side was the winner in the derby against Newcastle in October 2013, and he scored four goals in their final five league games of last season - including a winner against Premier League title chasers Chelsea at Stamford Bridge.
Borini also helped Sunderland reach the Capital One Cup final and scored the opening goal at Wembley, but ended up on the losing side as they were beaten by Manchester City.
The striker returned to Liverpool for pre-season and started in the club's first friendly, a 2-1 defeat away at Danish club Brondby on Wednesday, before a fee was agreed with Sunderland.
If he completes the move he will become Sunderland's fourth summer signing following the arrivals of midfielder Jordi Gomez from Wigan, defender Billy Jones from West Bromwich Albion and keeper Costel Pantilimon from Manchester City.