Dear Gottfried,

Thank you for your help and patience.

The presented object appears to be a painting made in oil or acrylic paint on canvas with the measurements of 122 x 152 cm. The painting depicts the boxing fight between Muhammad Ali and Aussie Joe Bugner. It is illegible signed on the reverse side and was made in the late 20th century.

Sadly no additional information about an artist fitting in style and motif is given by reference books and databases. 
Comparable objects were recently offered and sold on the international auction market. 
This piece is in good condition and there is no serious damage visible in the images provided.
A fair market estimation would be between 200 to 400 USD.
This estimate is based on actual recent past recorded auction sales of comparable items. Retail "asking prices" can be higher and may vary.

With kind regards,

George