Brad Pitt has reportedly purchased a motocross bike for his son Maddox's birthday.

The actor's adopted son with fiance Angelina Jolie turned 11 recently.

Brad is an avid motorcycling enthusiast and Maddox has apparently followed in his father's footsteps.

The star presented Maddox with a Suzuki DRZ-125 over the weekend.

"Brad's always been a generous dad and as Maddox has shown a keen interest in bikes, he thought he may as well get him started," a source told British newspaper The Sun.

"Brad took him into the garage and there the bike was with a bow on it. Maddox was over the moon and couldn't wait to try it out. He was riding it around all day at the house, tearing up the lawn."

Brad has also built an extensive motocross trail at the Chateau Miraval family estate in France.

"He was down at the house the other week and got the builders to dig him a muddy trail all through the woods and around the lake," the source detailed.

"Brad was just as excited as Maddox about it, though he's put in little jumps and puddles so they'll get really muddy."