His brother finally gave his approval and bought Choo a set of football equipment when he made Singapore's Malaya Cup squad.

The China national team selectors expressed interest in calling Choo for the 1940 Summer Olympics but the event was cancelled with the impending World War II.

[2][25] Choo stayed in Macau and China during World War II,[2] and wrote propaganda while an agent for the British as manager of the British-backed Macao Tribune.

[30] In 1952, Choo became manager and coach of SAFA Second Division Star Soccerites,[4] a club he founded.

[23] On 5 March 1957, the club opened their league season with a record 17–1 win over Royal Engineers Civilian Association.

[33] Choo left Star Soccerites in 1957 and joined Marine Department Sports Club, coaching them to the First Division title.

[34] Choo was appointed the first foreign coach of the Indonesia national team in 1951, which he held in an honorary position concurrent with his club duties.

[50] Right after extending his contract, Choo departed on a six-month coaching course in England where he was attached to champions Burnley[51] and other clubs like Everton, Sheffield United for the 1960–61 Football League season.

[52][53][54][55] The trip was made under a personal arrangement by FAM president Tunku Abdul Rahman[nb 4] with a British Council bursary.

[53] At the Southeast Asian Peninsular Games in December 1961, Malaya defeated Burma 2–1 and Cambodia 4–0 to top their group.

[57] Malaya scored two late goals in the final ten minutes to defeat hosts Burma 2–0 to win the football competition.

[63][64][65] Choo left Malaysia at the end of the Merdeka Tournament in September 1964[66] after he felt he was under-utilised in his coaching capacity.

[67] Choo had also rejected coaching offers from Japan, Thailand, Hong Kong and Indonesia during his time with the FAM.

[69] The next month, SAFA put in a request to engage Choo's services in training Singapore FA for the Malaya Cup.

[70] Tunku Abdul Rahman, the Malaysian Prime Minister and President of the FAM, approved Choo's secondment to SAFA in June.

[78][79] In December 1965, Singapore was eliminated at the group stage of the 1965 Southeast Asian Peninsular Games after losses to Burma and South Vietnam.

On 28 December, the SAFA sacked Choo with immediate effect and dropped six players from national team due to alleged misconduct and insubordination at the 1965 Southeast Asian Peninsular Games.

[80][81] He offered to assist in coaching the national team in June 1966[82] but was rejected by the Football Association of Singapore (FAS), formerly known as SAFA, which cited a lack of funds to pay his salary.

[89] In his time outside the national team set-up, Choo coached Police Sports Association from September 1968 and led them to the 1968 President's Cup.

The team defeated Hong Kong 2–1[92][93] and achieved a shock 1–0 win over pre-tournament favourites and 1970 Asian Games champions Burma.

In 1973, Choo rejected a coaching contract worth $2,800 per month, with first-class board and lodging, and free transport from professional Hong Kong club Caroline Hill FC.

[99] Between 1971 and 1975, Choo was also honorary coach of local clubs including Burnley United, Singapore Marble,[nb 8][100][101] Tampines Rovers,[102] and Farrer Park.

[103] On 2 September 1976, Choo was appointed to coach Singapore for the preliminary World Cup tournament in February 1977 in his 4th stint with the FAS.

[106] With the support of newly elected FAS chairman N. Ganesan, Choo was able to have non-interference in matchday selection of players for the first time.

In the play-off match on 12 March, Singapore lost 1–0 to Hong Kong to eliminate their chances of reaching the final qualifying round.

[109] Choo had announced his intention to relinquish his position after the play-off due to his advanced age and a need to focus on his business.

[16][113][116] Choo was praised for his tactical substitutes in the second half in which he replaced captain Samad Allapitchay and free-kick specialist S. Rajagopal with Lim Teng Sai and Nasir Jalil respectively.

[116] Following reported unhappiness of the players over the disparity in bonuses and mistreatment by the management leading to an alleged boycott of training,[117][118] Choo rejected a one-year contract offer by the FAS[112] and tendered his resignation on 27 June[119] but withdrew it after talks with the FAS and the national players.

[123] He returned to coaching with Malaysian outfit Johor FA midway through the 1980 season[124] but left the team abruptly in January 1981.

Players Edmund Wee, Quah Kim Song, Ho Kwang Hock, R. Suriamurthi, T. Pathmanathan were among the pallbearers.