Derby boss Nigel Clough hopes Jamie Ward is progressing and will be back in first team contention before the end of the month.
Ward has missed eight matches since he limped off during the 1-0 victory over rivals Nottingham Forest at the City Ground on September 30.
The Northern Ireland international will miss the trip to face Championship leaders Crystal Palace on Saturday and might not be fit for the home game against Birmingham a week later.
Clough said: "Jamie is coming along slowly, we hope it won't be too long. He won't be back until he is 100% because he got involved [in training] a few weeks ago and felt it again.
"We hope he can get a game for the Under-21s against Barnsley on Monday but we are going to take our time with him and it might be more towards the Birmingham game, or maybe just after."
According to SkySports.com, Pompey hope to land the experienced forward now, before adding him to their ranks on a full-time basis in January.
A deal will, however, depend on the success of a proposed takeover at Fratton Park.
The Pompey Supporters' Trust have edged a step closer to buying the League One club, with a deal agreed with administrators.
Should Portsmouth be able to find some much-needed stability, they will then be able to focus their full attention on efforts on the field.
Benson is considered to be the type of player who could aid them in their quest to secure promotion back into the Championship.
The former Dagenham and Charlton frontman is now 33 years of age, but he is a proven goalscorer in the Football League.
