The hardworking Cumbrian back-rower was released by Hull KR at the end of last season, after four years with the East Yorkshire side.
He was attempting to find a new club when Rhinos offered him the chance to train with them on a trial basis.
That means he will be fully fit should a club come in for him – and a deal with Leeds could be on the cards if he impresses coach Dave Furner.
Reflecting on a difficult few months since leaving Rovers, Donaldson insisted: “I said I am not going to let this get on top of me, I am going to stay as positive as possible and I did that.”
He stressed: “It is a tough situation; my life revolves around rugby. I moved away from Cumbria when I was 15 to play rugby and that’s what I live for.
“When it wasn’t there – and all the other lads were training – it was tough. It’s not the position I wanted to be in, but I knew my time as a professional rugby league player wasn’t up.
“I still knew deep down I had a lot to offer and that’s why I am staying as positive as possible. I am probably halfway through my career, but my body’s good and I feel fresh. I have had injuries in the past, but I am over them and I am just looking forward and hopefully I’ll get an opportunity soon.”
Donaldson linked up with Rhinos last week, initially until Christmas. He added: “It’s going great, I’ve settled in great. I know a lot of the lads here already, I live in Leeds and I’ve played against them for a long time when I was at Bradford.”
The 27-year-old has 115 Super League appearances to his name and was also a key member of the Hull KR side which topped the Betfred Championship table in 2017 before going on to win promotion back to the top flight.
Explaining how the trial came about, he said: “A friend of mine put a word in for me and also my agent spoke to them. A few things came together and Kev [Sinfield, Rhinos director of rugby] gave me a call and said ‘do you want to come down and train with us? We’ll have a look at you and take it from there’.”
Furner was a back-rower in his playing days and Donaldson feels he can only benefit from working with the former Test star, whatever comes of the trial.
“It’s new ideas and I’ll be learning something different,” he said. I think it puts me in the best possible position, either to go to another team or stay here. I am absolutely loving my time here.
“I’m fitting in great with the lads, I’m finally getting to grips with the systems they are running and I am really enjoying it.”
Though Furner has yet to name his team for the Wetherby Whaler Festive Challenge against Wakefield Trinity on Boxing Day, Donaldson confirmed he is eligible to play if selected.
Rhinos left number 25 vacant when their 2019 squad was announced last month, but Donaldson said: “I haven’t had any indication at all.
“I am just trying to keep my head down and let my hard work do the talking. If the club do decide to take me on that’s an even bigger bonus for me.”
Despite the unhappy end to his time with Rovers – having scored 10 tries in 77 appearances – Donaldson insisted there are no hard feelings.
He said: “I was disappointed. I had been there for four years, but I don’t hold any grudges. It is just business at the end of the day.
“They are doing what they have to do for the club to move forward and [it] obviously put me in a bad situation, but I have tried to keep myself active. I’ve kept myself fit and trained every day at the gym and tried to be as proactive as I could.
“I’ve been contacting coaches and clubs as much as I can and just waiting for an opportunity.”