"Graham Rodger and I had a meeting with the chairman on Tuesday," Groves told the club's official website.
"We stated that Phil was part of our plans, he was in the squad, and we wanted to keep him.
"With the long-term injury to Steve Livingstone and, to a lesser extent, the one to Robert Taylor, we have become short in the striker department.
"Phil was on the bench at Millwall and came on late in the game.
"The decision was taken purely for financial reasons. Obviously we're disappointed, but we appreciate the logic behind the decision.
"At the end of the day, everyone has to appreciate that the books need to balance.
"Matters such as this are no longer footballing decisions alone."