Currently on loan from Internazionale, Alvarez has made just 17 appearances for the Wearside club this term, although he has yet to appear under Dick Advocaat, having been suffering a knee injury since the Dutch coach’s appointment.
The injury is set to keep him out until the end of the campaign, and then Sunderland have to decide whether to take up their option to purchase him outright this summer.
The Argentine international certainly has the quality to succeed at the top level, but his failure to have a noticeable impact with Sunderland - only one goal and no assists in his season - has suggested that he is not cut out for the Premier League.
Leverkusen are now interested in him, and his poor season at the Stadium of Light may see Alvarez desire to play elsewhere next term.
However, it is stated that Sunderland still have hopes of securing Alvarez on a permanent deal, although they want a discount on the previously agreed price between them and Inter - a discount that Inter are against agreeing to.