Plymouth defender Mathias Doumbe and midfielder Simon Walton are both having a trial at Millwall.
Doumbe trained with the Lions on Friday and has been given permission to feature in their pre-season friendly date with Middlesbrough on Saturday.
The Frenchman is Plymouth's second longest-serving player behind goalkeeper Romain Larrieu, but he could be set to move on.
Out-of-favour Walton has also been training with Millwall this week with the hope of securing a permanent deal.
The 21-year-old, who has already turned out for eight clubs in his short career, could also be included against Boro.
"Mat trained with Millwall and we have given him permission to play in a game for them," confirmed Argyle boss Paul Sturrock.
"Walton has also been away with Millwall for the last three or four days. I don't know whether he will play for them. I haven't discussed it with Millwall yet."