The Iron remain bottom of League One after a 1-1 home draw with Sheffield United, though they should have claimed all three points after the visitors had two players sent off.
The home side still laboured before taking the lead when Clarke headed home minutes after coming off the bench.
"Leon is a good player. It has been a real struggle to find the strikers that we need, but Charlton have agreed to let him come here on loan," said Knill.
"But he and Karl Hawley who we have brought in will make us stronger. I am sure that they will now make us competitive."
Knill was left to rue a lack of concentration which allowed the visitors to come back and claim a point, despite trailing and having two less players.
"I thought we played well, but they have one chance and the ball finishes in the back of our net. That's the way it is going for us at the moment," he said.
"But there are plenty of positives to take from this performance. After four successive defeats, we did not want a fifth. We have got our first point on the board and we can build from there.
"We will be okay, we have something to build on now," he said. The circumstances at this club have changed from what they were and we are dealing with that.
"It takes time, but I have no doubt at all that we will be okay. We will be better than we were last season but it takes time to turn things round when we have made so many changes."
Danny Wilson, the Blades manager, insisted he would appeal the red cards shown to his players.
Michael Doyle was sent off quarter of an hour into the game after appearing to kick Iron forward Mike Grella in the head, while Ryan Flynn followed him into the dressing room after 72 minutes.
"We have been asked not to criticise referees but it it difficult to accept that when you get a performance like we have seen. It was an absolutely terrible game from this referee's perspective," he claimed.
"First he has sent Michael off for an alleged stamp, but he got nowehere near their player, he was a foot away from making contact.
"And then in the second half the referee has sent off Ryan. It was a situation where both players were going for the ball hell for leather. It was a booking at best, but the sending off was ridiculous.
"Of course we will be appealing against each red card and I just hope that the referee realises the mistakes he has made. If he does that, then he will come out of it a better man.
Wilson insists his side deserved to finish with a point to continue their unbeaten start to the season.
"It is not relief to come away with a draw, it's justice, I was so proud of the commitment of my players," he said.
"In difficult circumstances they have put their bodies on the line. No-one can question their commitment."