The 24-year-old New Zealander was shown red in the 87th minute of the National League North game.
“He was told by the steward twice not to do it and he went ahead and had a pee,” said Park Avenue secretary Colin Barker.
Crocombe later apologised, saying he has been in an “uncomfortable position” and made “an error in judgment”.
Writing on his Twitter account, he added: “My intention was never to offend anyone and I’d like to apologise to both clubs and sets of supporters.”
A spectator made a formal complaint and the incident was reported to the police.
Barker added: “He went to the side of the stand as I understand it. I didn’t actually see it, but the referee definitely sent him off for it because he was alerted to it by his linesman.”
During the game, Park Avenue tweeted: “We can confirm that Crocombe has been sent off for urinating during the game. We are not joking.”
Former Oxford goalkeeper Crocombe joined Salford in May. The club is owned by businessman Peter Lim and five former Manchester United players Ryan Giggs, Gary Neville, Phil Neville, Paul Scholes and Nicky Butt.
Salford reacted to the dismissal by tweeting: “Red Card! Crocombe sees red for something off the ball. No one has a clue what has happened.”
Earlier this month Giovanni Liberti was banned for five games for urinating at away fans in a Serie D game.