Roma appeared to have Malcom all wrapped up, with the former Bordeaux attacker due in the Italian capital on Monday evening to complete a routine medical and sign his official contract.
The two club's announced the deal had been agreed on their social media accounts but the Brazilian winger ultimately signed for Barca after they came calling at the last moment.
"What happened with Malcom is easy to explain but complicated to understand," the club's sporting director Monchi said at goalkeeper Robin Olsen's official unveiling.
"He was a player we liked a lot and had the profile we were looking for. We started negotiations with Bordeaux and his agent.
"After a few days of work, we found an agreement at five yesterday. The agreement had been found with his agent and Bordeaux.
"The French side had given permission to the player to leave, and he was due to arrive at 11 last night," he added.
"We were calm and convinced. Thirty minutes after the agreement with Bordeaux, my President called me telling me that it was better for them to make an official statement about the agreement.
"I knew there were so many teams interested in Malcom, including Barcelona, and it’s for that reason we found an agreement as soon as possible.
"My surprise is when one of his representatives called me and told me that Bordeaux had blocked his trip to Rome.
"At that point I called the Bordeaux President and he told me a better offer from Barca had arrived and that we had to at least match their offer.
"I told him we had an agreement, but he told me we hadn’t signed anything. I called Pallotta and he told me that we could make a higher offer, against my opinion.
"I called the president and told him we could make a better offer. The President said he needed the documents signed with the new offer and, when I sent it to him, he said Malcom would arrive the day after.
"At 11, his agent told me that there’d be a meeting to fix everything, but after midday they told me we had to make another offer because Barcelona was pushing.
"Therefore, I said 'that's it' because I didn't want to go into an auction. Yesterday we did it because of our President's wish, but we can't go any further.
"We're now considering whether to take legal action."