Frank Arnesen has confirmed that Chelsea are keeping tabs on Angel Di Maria, Fabio Coentrao and Javi Garcia.
The Blues, who are appealing an 18-month transfer ban, have been linked with the trio of Benfica midfielders since the summer.
All three youngsters are tied to the Portuguese club on long-term contracts and are valued at around 30million euros each.
Arnesen, Chelsea's sport director and former chief scout, admits it is far too early to speak about reaching any kind of deal.
But he insists it is important for the Blues to monitor any potential transfer targets despite the current embargo.
Asked about Di Maria, Coentrao and Garcia, Arnesen told Portuguese newspaper O Jogo: "These are good players and we need to know details about this type of footballer.
"This does not signify that Chelsea are preparing contracts but it is necessary to follow the market.
"The club awaits a decision over transfers and when we will be able to next reinforce the squad."
Benfica insisted this week they had not yet received any formal offers for their players.