Middlesbrough will make decisions on trialists Malaury Martin and Jurica Vranjes after the weekend.
France Under-21 international Martin and Croatia midfielder Vranjes are both out of contract and training with Boro.
Manager Tony Mowbray has been impressed with what he has seen from the pair, but will wait before making a final decision.
He the club's official website: "It's still early days and Jurica only arrived on Thursday. The French boy has shown up very well, he's a talented individual.
"We need to talk a bit more. We'll probably have some 11 v 11s at the weekend and we'll decide what we think after that."
Mowbray has left the door open for out-of-contract Argentine star Julio Arca to return to the club, and added: "His advisors will be looking in the market place to see what's available as close as he can to the salary he's been on for a few years.
"He's got to weigh up where he wants to live and quality of life for his family. I haven't had contact with his advisors for a few weeks but if they came back and were still looking and haven't had the offer they're looking for, we'd be interested."
Former Boro duo Stuart Parnaby and Graeme Owens, as well as Middlesbrough-born Chris Hogg, are training with the club to maintain their fitness.