The Glovers threw away a two-goal lead to draw 3-3 with Carlisle on Saturday and they have won just one of their last seven League One matches.
And with loan strikers Wes Fletcher and Jordan Cook having gone back to their parent clubs, the latter due to a knee injury, Johnson is weighing up his options before the loan window slams shut.
"There are lots of loans available and the reason why there are so many available is because not many clubs want them," he told the Western Morning News.
"It's very difficult to get a loan that gives you what you want because a lot of players are like that. They are just drifting through the game and drifting from club to club.
"They are good players but whether they go beyond the call of duty like you need at this stage you don't know.
"I have had a couple of loans in the past that are good players but I've not been pleased with their commitment to the cause."