Sinclair, 18 made his name last season whilst on loan at Plymouth Argyle in the Championship whilst he netted in the Blues 4-0 win at Hull City this season in the League Cup.
He also featured in their 1-1 draw against Manchester United in the Community Shield, the Red Devils won 3-0 on penalties with defender Phil Bardsley named as an unused substitute.
England U-19 international striker Sinclair is expected to join Sheffield United on loan.