The Bulldogs had five players missing as they crashed 56-14 at Halifax on Monday and problems were added to when prop Luke Stenchion went off after 15 minutes with a gashed head which required stitches. Despite this, he went back in the second half.
The Bulldogs have no game this weekend because of the Challenge Cup and Thornton said this would give chance for some players to get back to fitness.
He added a few harsh facts of financial life at National League level when he said: "Because of their own injuries, the top clubs are simply not releasing players on loan and that's before we can even get into a debate as to whether we can afford them. But if you want quality, you have to pay for it.
"We know we have to strengthen but so many clubs are in the same position. We have inquired around Super League and had a particular player in mind but last week his club suffered an injury in his position, they wanted cover and wouldn't release him.
"If we have a full-strength squad we can cope and we have perhaps 20 who can compete in Division One. If we have injuries, we are struggling and there isn't much we can do about it. We have played the Halifax first and Reserve teams and they have cover all over the park.
"We started the season so well but have hit a slump and are as low as we have been for some time. It puts onus on the players who are turning out to perform and that wasn't the case with some of them at Halifax. Even so we had our moments and scored three good tries from set-pieces but our defence simply wasn't good enough.
"We need time to develop the fringe players, unfortunately we don't have that luxury."
The Batley Reserves are at Workington on Saturday which gives a chance for some players to try and stake a claim for a senior place. Richard Colley will be in the team and also likely to play are threequarter Steve Laurie, who is back at the club, and Andy Boothroyd, who has returned after missing the last couple of weeks.
Scrum-half Paul Mennell was out of the Halifax game because of an ankle injury suffered in training last Thursday. Prop Byron Smith had an injured toe and was ruled out when he tried to train on Saturday.
Thornton remarked: "Paul Mennell's absence meant both half-backs were missing. At first we were able to cope without Francis Maloney but he is now being badly missed.
"At Halifax we discovered how important a quality half-back can be and Graham Holroyd destroyed us, six of their tries came from his kicks. We know what he is all about and what we have to do to stop him but we didn't follow it at all and some of the tries were embarrassing."
Thornton said the Bulldogs were still in the hunt, trailing only 18-8 but, for the third game in succession, they conceded six points just on half-time to put them virtually out of the running and too many heads dropped in the second half.
The Bulldogs have allowed second row man Anthony Thewliss to join Hunslet Hawks on a month's loan and he was in the side which gained their first win at Rochdale on Monday.