Tahir Ali, MP for Birmingham Hall Green, joined mourners in Sutton Coldfield, defying the strict rules on social distancing.
It has been reported the number in attendance on Wednesday was between 80 and 100, though most attendees dispersed after saying funeral prayers.
Police said "on arrival officers found approximately 15 people socially distanced into family groups, therefore no action was taken".
Only six people are currently permitted to attend funerals as part of the battle against Covid-19.
We warned Mr Ali about his behaviour and reminded him of the clear need for everyone to follow the rules surrounding social distancing and the guidelines that have been issued around funerals. (continued)— West Midlands Police (@WMPolice) April 3, 2020
Labour MP Mr Ali said he was there to "observe" after being contacted by the distressed family, who he knew well.
He has now apologised and vowed not to attend any other funerals after his actions were blasted as irresponsible by West Midlands Police and Crime Commissioner David Jamieson.
Police chiefs have now "warned" the MP about his "behaviour" in defying the guidelines.
West Midlands Police said: "Following recent media coverage of a large gathering of mourners at a funeral in Birmingham earlier this week, we can confirm that we have spoken to Tahir Ali MP about a suspected breach of coronavirus restrictions.
"We warned Mr Ali about his behaviour and reminded him of the clear need for everyone to follow the rules surrounding social distancing and the guidelines that have been issued around funerals.
"New restrictions have been placed on the numbers of mourners that can attend funerals in order to help stop the spread of Covid-19.
"We would urge people to check their local authority websites for guidance. It is vital people follow these rules."
Following criticism, Mr Ali said in a statement: "I apologise unreservedly for the confusion caused by my presence as an observer at a funeral in Sutton Coldfield on Wednesday.
"I will not be attending any other similar gatherings.
"I wholeheartedly support the Government's measures on social distancing to prevent the spread of coronavirus and urge everyone to follow them, in all our interests."