Rangers manager Mark Warburton believes that Celtic need the challenge of Old Firm games in the Scottish Premiership to stay competitive.
Celtic have eased to the Scottish title in the absence of Rangers in recent years, but of late have struggled in Europe, missing out on the Champions League group stage for the last two successive campaigns.
This term Ronny Deila's men have just been beaten home and away by Norwegian side Molde in the Europa League.
Warburton's Rangers are on course for a return to the top flight next season as they sit top of the Scottish Championship and the Englishman believes the Gers' return would be to Celtic's benefit.
"The better the challenge you face, the better the opportunity to develop and move forward", he told the BBC.
relatedNewsStory
"Any team, in any league, you require the quality, consistent challenge.
"I'm sure Celtic need that quality of challenge on a more consistent and regular basis to allow them to be successful at the high level", the former Brentford boss continued.
"I'm talking here as coming in from the outside."
And Warburton feels that teams from other European countries have an advantage because of the challenge they face in their own leagues, one which is absent in the Premiership.
"The European teams have that variety and quality of challenge and we have to make sure that Scottish teams have equally as good an offering of fixture."
Warburton's Rangers have won 12 of their 13 league games so far and sit five points clear of Hibernian in the Championship standings.
