Grabowski defeated Kiril Handzhiyski at FX3 on June 13 in London. Grabowski was then scheduled to fight PRIDE veteran Valentijn Overeem at a Beast of the East event in November in Gdynia, Poland and also Thorsten Kronz on December 5 in Darmstadt, Germany on Mix Fight Gala IX. Damian sustained a shoulder injury during training just a few days before the Overeem fight and had to drop out of both bouts. Grabowski then returned in 2008 with a first-round armbar win against Dion Staring and then fought in June against Michał Kita to determine the best heavyweight fighter in Poland. After connecting with a powerful upkick that cut the eyebrow of Kita, who slipped and fell out of the ring, Grabowski was declared the winner by doctor stoppage due to a heavily swollen eye. Grabowski won bouts with Stav Economou at MMA Attack 3, with Tadas Rimkevicius at M-1 Challenge 39, and with Kenny Garner at M-1 Challenge 44: Battle of Kulikovo. The last one was for the M-1 Heavyweight Championship. During M-1 Challenge 50, Grabowski fought against his friend, also the Polish fighter, unbeaten Marcin Tybura. Tybura managed to take Grabowski down early in the first round and won the fight by mean of the north/south choke. Surprised, Grabowski didn't spare the compliments for Tybura after the fight, as the championship belt left in Poland.
Bellator
MMAROCKS.PL first announced in 2010 that Grabowski signed a contract with the American promotion Bellator and would compete in their heavyweight tournament at Bellator XXV in August 2010. His opponent in the first round was Scott Barrett. Grabowski won the fight via unanimous decision. He was expected to face Neil Grove in the semi-finals, but instead faced Cole Konrad. His thirteen-fight winning streak was snapped, as he lost the fight via unanimous decision, being unable to stop the takedowns of Konrad, the future winner of the tournament. After defeating Joaquim Ferreira and Eddie Sanchez for the MMA Attack promotion, Grabowski fought one more time in Bellator in May 2012 where he defeated Dave Huckaba at.
After amassing a record of 20 wins against 2 losses, Grabowski was signed by the UFC to a contact. He debuted against Derrick Lewis on February 6, 2016 at UFC Fight Night 82. He lost the fight via TKO in the first round. Grabowski faced Anthony Hamilton on July 30, 2016 at UFC 201. He lost the fight via knockout in the first round. Grabowski was expected to face Viktor Pešta on January 15, 2017 at UFC Fight Night 103. However, Grabowski was removed from the bout on December 21 for undisclosed reasons and was replaced by Alexey Oleynik. Grabowski was expected to face Christian Colombo on May 28, 2017 at UFC Fight Night 109. However, the pairing was scrapped as both fighters sustained injuries in the weeks leading up to the event. The pairing was left intact and was rescheduled for July 22, 2017 at UFC on Fox 25. Subsequently, Colombo was removed from the fight on June 22 for undisclosed reasons and was replaced by Chase Sherman. Grabowski lost the fight by unanimous decision. On August 14, 2018, it was announced that Grabowski was released from UFC.
KSW
After knocking out Karol Bedorf to start his stint in KSW, Grabowski is expected to challenge Phil De Fries for the KSW Heavyweight Championship at on September 14, 2019.
