After posting a highlight reel on Instagram, he caught the attention of his future player agent, who informed him that Canadian Premier League club York9 was interested in him.[3] After feeling the opportunities at Toronto FC lacking, he left the club's academy and signed with York9 on May 13, 2020, with options until 2023, becoming the club's youngest ever signing.[5][6] After not making any appearances in the 2020 CPL season, he requested and was granted his release from the club.[7]
In December 2020, he returned to the TFC system, signing with Toronto FC II of USL League One for the 2021 season.[8] He made his debut on May 26, coming on as a substitute against FC Tucson.[9] He scored his first goal on June 19, against Fort Lauderdale CF.[10] In October 2023, he signed a short-term loan with the Toronto FC first team, ahead of their match against Charlotte FC.[11] In March 2024, he re-signed with TFC2 for the 2024 season.[12] In 2024, he signed another three short-term loans with the first team.[13][14][15] On July 14, 2024, he became the all-time appearance leader for Toronto FC II, with his 85th cap across all competitions.[16] He was awarded the MLS Next Pro Goal of the Matchweek twice that season.[17][18] On September 15, 2024, he scored in his eighth consecutive match (the second longest streak in league history),[19][20] netting his 20th goal for the club, tying him for the club all-time lead with Jordan Perruzza.[21] Altobelli's contract expired following the 2024 season.[22]