Michael told us yesterday he was gonna do the concert -- the one with Janet and the Jackson 5 in Texas in 2010 -- but the CEO of the company planning to throw the concert thinks Jacko's word is worth nothing.
Patrick Allocco told us his company will sue M.J. unless the singer signs on the dotted line, promising to sing with his sister and his bros.
Jackson has balked at doing the family concert, favoring his London gig ... which could be in jeopardy.
UPDATE: We just received the following comment from Allocco, "Let me say this as clearly and unequivocally as I possibly can ... I have spoken with Michael Jackson and I believe that he is an honorable man. A man of his word. I look forward to working with him and his entire family on the historic show we have been planning for more than a year."