Derby manager Nigel Clough has invited experienced midfielder and free agent John Eustace to train with his squad.
Eustace, a former Rams loanee, is a free agent after his contract with Watford expired.
The Hornets wanted the 33-year-old to remain at Vicarage Road in a coaching role but he is not ready to hang up his boots and has offers from other clubs on the table.
Clough told the Derby Telegraph: "John is training with us. He has a couple of playing offers from clubs but we have said 'come and train with us for a couple of weeks and see how it goes'."
Eustace spent the final two months of the 2008/09 season on loan at Pride Park from Watford.
Former Gulls striker Benyon spent three and a half years at Plainmoor before leaving for Swindon in 2011 having scored 39 goals in 125 appearances.
The 25-year-old returned to the Devon club on loan from Southend at the end of last term and boss Alan Knill has moved quickly to make the deal permanent following his release from Roots Hall.
"He was brilliant at the end of the season," Knill told the club's official website.
"I think everyone saw that the longer he was here, the better he became and the fitter he became."
Former Rotherham right-back Tonge will also play in blue and yellow next season after completing a deal following discussions with the club last week.
The 28-year-old had been a regular for the South Yorkshire side until a persistent injury limited his appearances last season during the Millers' promotion campaign.
