Transfer journalist Matteo Moretto confirmed all three Serie A clubs have been tracking Dieng closely, with head coach Maurizio Sarri understood to be personally interested in adding a mobile, pressing centre-forward to Lazio's attack.
Dieng has scored nine Ligue 1 goals and five further goals in the Coupe de France — 14 in total across all competitions in 24 appearances. He missed the first part of the campaign with a ligament injury but has been Lorient's undisputed first-choice striker since January, scoring with consistent regularity in the second half of the season.
The 6ft striker can operate as a centre-forward, second striker or wide forward and has previously played for Olympique de Marseille before joining Lorient. He has earned 21 caps for Senegal, scoring twice.
His availability as a free agent is the central attraction. Lorient had initially valued him at between €12million and €15million, a figure that has reduced to zero given the contract situation. All three Italian clubs are in a position to offer him terms immediately — though Torino face a specific complication as Dieng does not hold an EU passport and the Granata have limited non-EU registration slots available.
St. Pauli in Germany and Real Betis in Spain have also been credited with interest, while English Championship clubs have made preliminary checks. The competition for a player who is available for nothing is likely to intensify once the season concludes.
Lazio face Inter in the Coppa Italia final on Wednesday. Their summer planning will be shaped by whether they secure silverware and the European football that may accompany it. Dieng, arriving for free, would represent a low-risk addition regardless of what competition they play in next season.