Tony Blair has advised British Airways "some battles are not worth fighting" when asked about its ban on cross necklaces being worn over uniforms.
Nadia Eweida had challenged the ban on her cross necklace
BA has been criticised by some MPs and church figures but an internal appeal ruling backed its refusal to exempt a cross from a visible jewellery ban.
BA's Martin Broughton asked about it at a CBI conference, pointing out similar rules in the police and armed forces.
Mr Blair said: "You're best just to do the sensible thing, know what I mean?"
He sidestepped Mr Broughton's specific question about whether he thought the uniform policy for police and armed forces was "wholly inexplicable" - the way Commons leader Jack Straw described BA's policy last week.
Mr Blair replied: "If you want my really frank advice on this: one of the things I have learnt in politics is there are battles really, really worth fighting and there are battles really, really not worth fighting.
"All I would say to you is get the right side of the line on that one. That's my honest advice."
He added he was "a fan of the airline and a fan of its management".
"There are some things, they arise in a certain way, and you're best just to do the sensible thing, know what I mean?" he said.
The row erupted when staff member Nadia Eweida challenged the ban on her visibly wearing a cross necklace while she worked at the check-in counter at Heathrow.
Ms Eweida had lost her appeal but can appeal again. Late last week BA announced it would consider allowing religious symbols worn as lapel badges.
Mr Broughton told the BBC he would pass on Mr Blair's comments to fellow directors who are carrying out a review of the company's policy on jewellery.
Mr Broughton said: "A lot of commentators have made the point that we live in a country of a Christian heritage and it is only a little cross, so just do the common-sense thing.
"My point was that just doing the common-sense thing is illegal under the discrimination acts, without going a great deal further. That's the complication I was referring to.
"We are not only talking about major religions here, the discrimination goes for any conceivable minority sect that you can talk about. I just wonder whether that's where the country really wants to go."