[6] On 10 August 2018, Collier joined USL Championship club Indy Eleven on loan for the remainder of the 2018 season.

[9][10] Collier returned to his parent club at the conclusion of the 2019 season, signing a new contract under new head coach Raphaël Wicky.

Collier made one substitute playoffs appearance for San Antonio, coming on in the 97th minute of the team's 3–1 victory over Louisville City in the final.

[15] Collier ended the season with two goals and three assists, with San Diego in third in the Western Conference, qualifying for the playoffs.

[22] Collier was born in New Zealand to an English mother and Kiwi father, and was eligible to represent both national teams.

[24] Collier was a close friend and teammate of New Zealand futsal player Atta Elayyan, who was murdered in the Christchurch mosque shootings on 15 March 2019.

[25] Collier wore a black armband in remembrance of Elayyan in a 1–1 draw with Loudoun United the next day while on loan at Memphis 901 FC.