Scott McDonald: "It was a massive move. I had to sit and really have a long, hard think about it, especially with the family.
"Celtic was a club I supported growing up, I was brainwashed into it by my Glaswegian parents, so it was quite difficult.
"It was a massive honour to play for the club for two and a half years and is something I will always treasure and always have with me.
"I leave, I would like to think, with a lot of success under my belt. Hopefully I can do the same for Middlesbrough and help us get promoted.
"Obviously, it was a big decision for me to leave. I have been there from being 14, so you make a lot of good friends at the club and played with some wonderful players.
"As a footballer everybody is different and you want to win things. When you are brought up at Celtic you have got a winning mentality for trophies and the chance to play in Champions League games.
"In that instance, it was a big decision. But with Gordon Strachan in charge, that was a big factor for a lot of the players.
"It's a fresh challenge for us all and it's one we are looking forward to."