The Boro boss brought in over a half-a-dozen new faces last summer, and they started the season in excellent fashion - even going top towards the end of 2012.
But for the second successive season, the Teessiders have seen their promotion charge implode after a shocking start to the New Year.
Now with promotion back to the Premier League appearing to be little more than a mathematical possibility - Mowbray is already looking at a potential overhaul.
"We ain't going to be able to keep this group together," said Mowbray.
"There's four, five or six players out of contract in the summer and some of them won't be getting kept on for various reasons.
"Some of that will be issues with salaries, some will be because we feel it's time for a fresh start. Some will be to do with trying to create a gap in the budget to release a salary to bring someone else in. So I think the terminology I'd use is that we're still trying to build a squad that we feel can grow together.
"If you look at the changes from the day we walked in to where we stand today, there's been a huge turnover in footballers. Is the team any better than it was when we arrived? You know, I think that's possibly open for debate in my mind.
"And yet, after our first game we found ourselves second bottom of the league and, in our defence, we've been in the top six all year apart from the last two months.
"So that would suggest that maybe we are a better group, not as players, as individuals. It means the chemistry of the group. But the job is forever to try and improve, to try and get better at every opportunity you can.
"The next time to improve on what we've got would be the summer when some contracts run out and there's potentially a hole in the budget to fill.
"That's not guaranteed, of course, because sometimes when players leave there might be a natural reduction in budget levels, so we'll see what the summer brings."