The Mariners are currently on a run of just three wins from 12 league outings.
Fenty has backed Newell to shake up his squad and told the Grimsby Telegraph: "You can't continue to change the manager year on year and get on that merry-go-round.
"Like I said in the statement, any player thinking they can hold on for a few games and there may be a change of manager are mistaken.
"The board supports the manager fully and ultimately it is he who makes decisions on the players and we support him after that.
"It's too early to say whether anyone will have their contracts paid up but to some extent the idea of bringing in new faces will see players go out to offset costs, even on loan."