The pair took the pitch for a kickaround before expressing their admiration for Lionel Messi and sympathy for Neymar, whose 2014 World Cup was ended by injury
The pair, who are in town for the latest leg of the boyband's 'Where We Are' world tour on Tuesday, were invited to the iconic arena by the Catalunya club.
Tomlinson and Horan were only too happy to accept and, after being presented with official Barca strips with their respective surnames on the back, took to the hallowed turf for a kickaround.
"It was incredible to walk onto the pitch," Horan enthused. "I have been here a few times before, and it’s nice to be back.
"This is one of the best stadiums in the world, and it was incredible to get the chance to walk out onto the pitch.
"The best players, for me, are Neymar and [Lionel] Messi."
Tomlinson admitted that he, too, is a massive fan of Barca's star duo, and sent his best wishes to the Brazilian, who saw his World Cup ended by injury against Colombia in the quarter-final stage.
"We all obviously love Messi, but it’s also fantastic to watch Neymar play," the former Doncaster Rovers reserve mused. "What a shame Neymar’s injured. He’s a brilliant player."