Elton John Cancels Vegas Concerts -- I Was Poisoned!

Elton John had a crappy weekend ... a very crappy weekend ... because the Rocket Man came down with a nasty case of food poisoning ... TMZ has learned.

E.J. was supposed to perform at Caesars Palace in Vegas this past Friday and Saturday night ... but the singer had to back out when something he ate ... backfired.

Elton's rep tells us John is doing "much better now" ... and will be ready to go in time for his next concert later this week .... in Guadalajara, Mexico.