Zander Diamond will definitely be ineligible for Cobblers selection for their home game against his parent club Burton Albion on Saturday (3pm ko).
The central defender has become a key player for Northampton after arriving on loan from the Brewers in February.
Although there are no rules in place to prevent players from lining up against the club who holds their permanent registration, Diamond will not be allowed to play.
“We understand that and respect that,” said manager Chris Wilder, who is also without suspended midfielder Darren Carter. “We knew all along that would be the case and we’ve planned accordingly.”
There is a rule against players playing against their parent club but only in the Premier League and FA Cup.
The Football League have a slightly different approach in that while it is standard that the loan player cannot play against their parent club, permission can be given in order for this to happen, except in FA Cup ties.
Cobblers fans will recall a time when Bristol City allowed striker David Seal to play against them for Northampton in August 1997 - and he scored in a 2-1 win at Sixfields.