Federer was due to play his opening match yesterday but rain caused havoc in Rome.
The Swiss star returned to the Italian Open grounds today knowing he will have to play twice if he beats Sousa.
But when he stepped onto centre court the stands were barely half full.
It is extremely rare that the 20-time Grand Slam winner does not play in front of a sold-out crowd.
Only Wednesday ticket holders were let in to watch the first two matches today – which Federer was second on court.
Supporters were furious yesterday when they were informed there would be no refund on tickets, despite prices being doubled when Federer’s appearance was confirmed.
And they failed to turn up this morning as Federer attempted to book his third-round spot.
Fans who had tickets for Thursday morning would only be allowed into their allocated seats for the third and fourth matches.
However, they were permitted into the grounds to catch some exciting matches which were forced onto the outer court.
But the majority of those who were let down yesterday did not take up the tournament’s offer of returning this morning.
And tennis commentator Rob Koenig believes he knows why.
“There is definitely a sense from these fans that even though they have been let in to watch Roger Federer play, they are being short-changed,” he said on Amazon Prime.
Federer and Sousa are playing to face Borna Coric later today.
Meanwhile, Rafael Nadal was made to kick-start his Rome campaign on Grandstand.
If victorious against Jeremy Chardy, the Spaniard will play his third-round tie on centre court.