Conservative MP Andrew Mitchell said he "did not believe" allegations against Deputy Commons Speaker Nigel Evans.
Mr Evans was arrested on suspicion of raping one man and sexually assaulting another between July 2009 and March 2013. He said the allegations are "completely false".
Mr Mitchell told BBC Radio 4's Today programme:
If he were to resign now we would be in a terrible position where every public office holder would be open to blackmail and false stories in the media, triggering their resignation.
Nigel Evans has been a friend and colleague of mine for more than 20 years, I have known him in good times and in bad times and I certainly do not believe these allegations.
I think he should definitely continue in that role. We have three deputy speakers in the House of Commons so if necessary there can be a degree of burden- sharing.
He has not been charged, he has not been found guilty, and we do still live in a country where you are supposed to be innocent until proven guilty.