Capped by Scotland at youth and schoolboy level, Sinclair joined Nottingham Forest as an apprentice from Stirling Boys Club and he signed professional forms in October 1982. However he failed to make a first-team appearance for the City Ground club and it was in a loan spell with Fourth Division side Wrexham in the closing stages of the 1983–84 season that Sinclair gained his first Football League action. Over the following two seasons he spent time on loan with Derby County, Sheffield United and Leeds United without making the first-team, but he was snapped up on a permanent basis by Leeds in June 1986 for £10,000. He made eight league appearances the following season before twice joining Halifax Town on loan.
