Collins collided with Umaga in the air and was down receiving treatment for some time before being shown a red card by referee Matthew Carley.
Umaga was taken off by Wasps as he also needed medical attention.
Saints went on to win the game 35-31, despite Collins' red card and a yellow for Cobus Reinach, as Taqele Naiyaravoro scored a decisive try three minutes from time.
And on Sunday evening, Collins delivered a classy gesture, taking to Twitter to wish Umaga well.
Collins tweeted: "Glad @jacob_umaga98 is ok after the game today. I did not mean to cause any dangerous play or put anyone in harms way. It all happened very quickly and I am sorry for my actions. All the best for the rest of the season mate."
Umaga replied: "No worries mate, part of the game! Glad you're all good too."