The Scottish international has failed to make the expected impact with the English Championship club and was rumoured to be on his way out of Teesside.
Now he is determined to add to his tally of just six goals so far this term.
"It's fair to say it was an unsettling month. I'm not fully blaming things on the transfer window - my form hasn't been good enough, there's no two ways about it, but at the same time it's not easy to listen to speculation constantly linking me away," he said.
"From a couple of months before the window opened all the way through, it was there, and now it's shut it's time I worked hard into the summer and see what happens then.
"I know myself that I've not been good enough but it's not been easy.
"I didn't know what was happening and I knew the situation we had here and that Middlesbrough were trying to offload people.
"I've enjoyed my time here and I think it's about time I got my head down and repaid the faith they've shown in me, to bring me here in the first place, we need to work hard and start climbing the table."