Donaldson signed for hometown club Newcastle aged nine and was fast-tracked through the Magpies' youth system. Ryan appeared for the reserve side at just 15 years of age and became their captain less than three years later. The Newcastle-upon-Tyne boy worked his way into the United first team towards the end of the 2008-09 season, but was an unused substitute on a number of occasions as his side were relegated from the Premier League.
Newcastle's subsequent one-season stay in English football's second tier offered Ryan his chance in the senior squad; he made his debut in a win over Leicester City in August and made five appearances in all. After one more appearance for Newcastle, he headed out on loan to Hartlepool United in 2011. Impressive showings in a one-month deal led to a loan extension by an extra month, playing 12 times in all before just the one game on loan at Tranmere Rovers.
A right-footed player with excellent ball-striking ability, Ryan signed for Gateshead in 2012 after his release from Newcastle. A week after signing, he netted his first senior goal in a 2-1 win over Stockport County, and his impressive form soon earned Donaldson a contract extension. Eight goals and plenty more assists in 43 games was enough for other clubs to take an interest in Donaldson. The England Under-17 and Under-19 international departed the Tynesiders after a single campaign to join an ambitious Cambridge United side with genuine hopes of a return to the Football League.
Ryan would have a memorable opening season with the Amber Army, receiving the Man of the Match award in two visits to Wembley Stadium. He first scored two of Cambridge's four goals against Gosport Borough in the FA Trophy final, before scoring a free-kick in the Conference play-off final against the team he departed: Gateshead. A midfielder with the ability to play centrally or on the flank, Ryan remained an important part of the United first team upon their promotion to League Two. He started their first game of the season - a 1-0 win over Argyle - and made 37 more league appearances that campaign, scoring five goals. Thirty more league games followed last season, playing more of an 'impact substitute' role upon the arrival of new manager Shaun Derry in November 2015. Donaldson left the U's at the end of the 2015-16 season, falling two games short of making a century of appearances, scoring 17 goals from midfield.