And the new Donny manager added Paul Downing could fall into the same category as he looks to bolster his squad ahead of the relegation battle that awaits his newly-inherited side over the second half of the season.
Danny Cowley is keen to generate extra funds in a bid to finance a recruitment drive of his own this month – and with the duo currently on the fringes of his first team, and out of contract at the season’s end, the Blues would be open to parting ways with the former Rovers pair.
Their wages will prove a factor, though.
Marquis is one of Pompey’s top earners after arriving from Doncaster for £1m in the summer of 2019.
McSheffrey is convinced the 29-year-old, who scored 66 times for Donny in 153 appearances before his move to Fratton Park, would provide the goals he desperately needs.
Bottom-placed Rovers’ current League One tally of 13 goals is the lowest in the EFL.
Yet he suggested Marquis’ salary would ‘eat up’ his whole budget.
‘John is brilliant,’ the Rovers boss told the Doncaster Free Press.
‘He’s a great player and I’m sure he would come here and guarantee some goals.
‘But Portsmouth aren’t just going to give him away. They’re going to want to recoup a lot of his salary.
‘John’s alone would probably eat up the whole budget that we’ve got.
‘We feel with the money available we could get four good additions in and you’ve got to weigh it up.
‘John would be great but realistically he’s going to be too expensive.’
On Thursday, The News revealed that Downing was an option for Doncaster as they attempt to shore up a defence that has conceded 39 goals so far this season in the division.
The 30-year-old has endured a nightmare spell at Fratton Park, making just nine league starts since arriving from Blackburn in the same transfer window as Marquis.
His potential departure could allow Cowley to buy the centre-back he desperately wants, with Stevenage also keen.
But McSheffrey admitted that finances could scupper any move back to the Keepmoat.
‘He’s been on the centre back list,’ added the Donny boss.
‘He’s not been our number one target.
‘On the list, he’s probably the one that’s earning the most money so it would be quite an expensive loan and it would eat up quite a lot of the budget.
‘He’s not on the top end of the list but he’s definitely been spoken about in the last month or so.’