Aston Villa's team bus was attacked following the club's Premier League match against Burnley FC on Sunday.
A brick was thrown at the bus from a footbridge as it travelled along the M65 near junction 10.
Nobody was injured in the attack but the bus was damaged as the brick struck the windscreen.
Supt Melita Worswick, of Lancashire Police, said: “This incident occurred when a great deal of traffic was leaving the area following the football match between Burnley and Aston Villa. It is nothing but good fortune that the brick didn’t cause more damage, or result in somebody being seriously injured or even killed."
“We cannot say at this point whether this was a targeted attack but enquiries are ongoing and this will form part of our investigation.
“We are now determined to find the person or people responsible and are asking for anyone with information to get in touch. If you have any information or dashcam which can help us, please contact us as soon as possible.”
Burnley FC says it is "saddened" by the news.
"We strongly condemn this behaviour and will support Lancashire Police in their efforts to find whoever was responsible"
Promoted Burnley were beaten 3-1 by Villa in what was their second Premier League match of the campaign. They are yet to collect a point.