Liverpool won the game 2-0 thanks to goals from Naby Keita and Roberto Firmino. However, they could have finished the match with 10 men and been without their star man for the return leg, had Salah been red carded in the 84th minute.
The Egypt international caught Danilo midway down his shin with a studs-up challenge.
"Danilo should thank God because this is a leg-breaker -- not trying to kick the ball," Da Costa said after the match. "I thank God he does not have a broken leg."
Da Costa said he was disappointed to see one of his players booked for a similar challenge, while referee Antonio Mateu chose not refer Salah's to the video assistant referee.
"We want equality for everyone -- look at Felipe's tackle which brought a yellow and this [tackle by Salah] for which we are lucky Danilo is not en route to hospital," Da Costa added. "We can score two goals just like we conceded here.
"The first was the first time Liverpool passed the halfway line and with a deflection.
"We continued to chase the goal, we had chances, there was a penalty which was not given for handball -- just look -- and Felipe was also caught."