The British Museum itself holds a fine collection of Rubens drawings, with a key focus on his depictions of the animal anatomy. Much less is known about his sketch work than his large scale oil paintings, so a certain amount of piecing together bits of information is required.
This sketch of a lion has a date attributed as circa 1620 which fits with his other animal drawings that all came around this time. His sketches of horses, bulls, cows and this lion were all from around this time.
Whilst similar to the other works mentioned, this depiction of a lion features a particularly stronger contrast which gives a more threatening look to this creature. White elements are use, possibly chalk, to contrast against the darker areas which tend to be on opposing sides of the lion's limbs and head.
The vast majority of Peter Paul Rubens' drawings were study pieces, not meant as artworks for sale in themselves, just a display of practice for later artworks in other mediums. These could be paintings, tapestries or architectural work. This sketch clearly relates to his larger oil painting of Lion Hunt from 1621. That oil on canvas remains in the Alte Pinakothek in Munich alongside a fine selection of paintings by Rubens.
Typically, Rubens' drawings would be small, probably putting them together in a small sketchbook as William Turner would do many centuries later. As such, this artwork is just 43cm by 28cm.