However, the logo was displayed so briefly that it was difficult for the worldwide audience to catch.
But by looking at a photograph of the moment, we see what Messi was trying to tell the world:
The t-shirt reads 'Sindrome X Fragil', which is the name of a medical condition known in English as Fragile X Syndrome.
Fragile X Syndrome is a genetic problem that leads to emotional, mental, and sometimes physical problems in its sufferers, with some of its effects being compared with those of autism.
Messi treats the syndrome as a personal cause, having during last month spent a day in Barcelona with children who suffer from the affliction.
As the player himself explained, he suffered from hormonal problems as a child, and had he not received help he could never have been in a position to score a vital goal for one of the world's top clubs.
Players often talk about giving something back, and with tonight's show of publicity it looks like Messi is serious about doing just that.
Ewan Macdonald, Goal.com