Caretaker-manager Dean Austin, who has taken over first-team affairs at the League One club following the dismissal of Jimmy Floyd Hasselbaink, has revealed that he made the move in an effort to circle the wagons and ensure that everybody in his team is committed to fighting relegation this season.
The Cobblers are in the drop zone of the third tier and in danger of going down to League Two as a consequence of the nine straight defeats that cost Hasselbaink his job.
"I made the decision about Boris," Austin is quoted by the Liverpool Echo as saying over the weekend after Mathis's final appearance for Northampton, a 20-plus minute cameo in a heavy home defeat to Charlton Athletic.
"You have to make decisions as a manager that you think are going to help the group," he explained, with the inference being that, in Austin's view, Mathis's heart was not in the battle to keep Northampton up. "I need people around who want to play for this football club, players that will give their heart and soul and every last drop of sweat and blood for this team and do what they've got to do to get the results we strive for."
Mathis was signed by David Unsworth last summer from Metz for Everton's development side. He suffered an injury early in his Blues career before being loaned to Northampton earlier this year to gain first-team experience.
Now back in Merseyside, he played in the U23s' 4-0 home reverse to West Ham last night, a game that also saw Shani Tarshaj play the first 45 minutes in his first taste of action in a Blue shirt since recovering from knee surgery.