Cullen, a huge favourite with supporters following a string of impressive performances, penned an extension to his loan deal from parent club West Ham United on Tuesday to keep the 20 year-old at the Northern Commercials Stadium until the end of the season.
With Cullen arguably playing as well at the moment as he has done throughout his two loan spells with the Bantams, the news of the midfielder extending his stay at City was understandably greeted with great joy by fans.
Speaking ahead of Saturday's home encounter with Chesterfield in Sky Bet League One, McCall says he was equally as delighted to retain the services of the Republic of Ireland Under-21s midfielder.
McCall said: "Josh has been consistently one of our top performers throughout this season.
"In particular over the course of the last three games, he has been outstanding.
"He has an old head on young shoulders. He is a great talker in the dressing room and a fantastic professional.
"He has great desire to keep playing and doing the right things.
"You look at him with five minutes or so to go before the end at Northampton, you wouldn't be able to tell that he'd played 90 minutes against Bury just 48 hours earlier.
"It would have certainly been a blow to lose him. Josh was keen to stay, he would obviously keen to keep him, so it was just a case of getting the new extension confirmed with West Ham.
"We are naturally delighted to keep him here until the end of the season."
With Cullen's place in McCall's squad secure for the rest of the 2016/2017 campaign, the Bantams chief says the club now hope to add further recruits to the ranks.
McCall added: "We've lost Haris (Vuckic), Marc (McNulty) and Nathan (Clarke) recently so we would like to add some more numbers to the group.
"We don't really need to strengthen defensively, despite Nathan's departure, but we are looking for players in more attacking areas.
"We are a bit thin on the ground in that area, especially with Filipe Morais and Billy Clarke being out injured, plus Haris and Marc having gone back.
"We are keen to increase our attacking options so we are looking to get at least one or two new faces in as soon as we can."