Atletico boss Diego Simeone was pelted with missiles including bottles after the final whistle at OId Trafford.
Uefa is waiting for reports from match observers before deciding whether to charge the club.
Throwing objects onto the field of play is against ground regulations and subject to a three year ban.
Ralf Rangnick's side were knocked out the Champions League following a 2-1 defeat on aggregate to the Spanish club.
The result thwarted United's hopes of ending a five-year trophy drought, meaning they are on their longest run without silverware since the period between FA Cup wins in 1977 and 1983.
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!