Teams will have to stick with that they have, after being able to sign players since January on loan deals, but after March 23rd this won't be the case.
Shirtliff has said: "I would have thought that no-one would be coming in before the end of the season.
"We have a good enough squad to do the job for the last few games of the season."
Shirtliff is now tryng to get players who are out of contract in the summer, to sign longer deals, as he looks to build for next season.