McDonald was born in London, and joined Fulham's academy from Crystal Palace as a 12-year-old. Through an arrangement with the club, he attended Coombe Boys' School in New Malden, Surrey. He was a member of the England under-16 training squad ahead of the 2012 Victory Shield, but a serious knee injury prevented his participation and kept him out until the following summer, when he took up a scholarship with Fulham. Their academy director described him as "a central midfield player who always looks to break the play up and get us moving forward can chip in with a goal or two as well."
Birmingham City
Later that year, he transferred to Birmingham City where he continued his scholarship. At the time, academy coach Steve Spooner described him as "only small" but "a really powerful boy who has an eye for goal likes to take people on". In late 2014, McDonald suffered a knee ligament injury that restricted his progress, despite which he was given his first professional contract, of two years, in May 2015. He was by then playing in a more advanced role: according to Spooner, he could "play on either flank or off the top. He has good levels of skill, he's very powerful and possesses a great engine. He has pace and scores goals as well." In his first senior season, McDonald played regularly for the club's under-21 team. On 12 February 2016, he joined National League South club Nuneaton Town on a one-month youth loan, following Birmingham teammate Kyle McFarlane whose loan expired the same day. He went straight into the starting eleven for the next day's visit to Brackley Town, and provided the assist for Elliot Whitehouse's goal that secured the team's first win of 2016, before being replaced after 87 minutes. He made four appearances, all starts, during his month. After his return to Birmingham, he appeared as a substitute for the reserve team that lost the 2016 Birmingham Senior Cup final to National League North champions Solihull Moors. He played regularly for Birmingham's under-23 team. In February 2017, coach Richard Beale commented that over the previous few months, McDonald had "really twigged that you have to work really hard without the ball as well", and his development was such that the club confirmed their intention to extend his contract. Towards the end of the 2016–17 season, after McDonald had produced a scoring streak of six goals in five matches for the under-23 team, manager Gianfranco Zola named him as one of the younger playersothers named were Corey O'Keeffe and Jack Storerwho would be given a chance of first-team football once the team were sure of avoiding relegation to League One. He finished the season as top scorer for the under-23s, but Birmingham's failure to avoid relegation until the final match meant any first-team debut remained on hold. The club took up the one-year option on McDonald's contract for the 2017–18 season, and in September, he spent a month on loan at Solihull Moors, where he played five National League matches and one in the Birmingham Senior Cup. He was unable to break into Birmingham's senior squad, and in February 2018, the club confirmed that he would be released. In March, he had a trial with Queens Park Rangers which came to nothing.
Yeovil Town
On 3 August 2018, McDonald signed a short-term contract with League Two club Yeovil Town, to run until January 2019. He was an unused substitute on the opening day of the season, and made his Football League debut a week later, starting and playing the whole of a 2–2 draw at home to Mansfield Town. On 3 January 2019, having failed to agree a new contract with Yeovil, McDonald was released upon the expiry of his short-term contract.
Walsall
McDonald signed a short-term contract with recently relegated League Two club Walsall in July 2019. Away to Crawley Town on 28 September, McDonald supplied the cross for Elijah Adebayo to put Walsall 2–0 ahead and then "cut in from the left-wing and curled a beautiful effort into the far corner" for the first goal of his senior career to make the score 3–1; Walsall won the match 3–2. His deal at Walsall was extended until the summer of 2021 on 7 January 2020.
