Anthony Joshua’s world title defence against Kubrat Pulev is in doubt after reports emerged on Monday night that the Bulgarian has suffered an injury.

The heavyweight challenger is believed to have strained muscles in his right shoulder during a sparring session 10 days ago but kept the injury out of the public domain.

Promoter Eddie Hearn was similarly not told about Pulev's injury, The Sun reports.

Anthony Joshua's career in pictures Show all 23 1 /23 Anthony Joshua's career in pictures Anthony Joshua's career in pictures Anthony Joshua's career in pictures After 22 professional fights, Anthony Joshua boasts an unblemished career record Getty Anthony Joshua's career in pictures Emanuele Leo, TKO (R1) 2:47 In his first fight since turning professional, 23-year-old Joshua floored Emanuele Leo in a vicious two minutes and 47 second rout. Getty Anthony Joshua's career in pictures Paul Butlin, TKO (2) 0:50 Joshua’s needed only two rounds to see off Paul Butlin in his second professional fight when the referee called an end to the tie 50 seconds into the second round. Getty Anthony Joshua's career in pictures Hrvoje Kisicek, TKO (2) 1:38 It was yet another second-round stoppage victory for Joshua, knocking out veteran Hrvoje Kisicek after a fiery flurry of punches on the ropes. Getty Anthony Joshua's career in pictures Dorian Darch, TKO (2) 0:51 Joshua demolished fellow Brit, Dorian Darch, landing multiple crisp blows in the opening minutes and leaving him the referee no choice but to put an end to the fight. Getty Anthony Joshua's career in pictures Hector Avila, (KO) 1 2:14 Joshua needed a mere 134 seconds to see off the challenge of Hector Avila in Glasgow and clock up his fifth win without defeat. Getty Anthony Joshua's career in pictures Matt Legg, KO (1) 1:23 Matt Legg was the next victim of Joshua’s phenomenal run. A venomous uppercut to the chin floored Legg in only 83 seconds. Getty Anthony Joshua's career in pictures Matt Skelton, TKO (2) 2:33 Needing less than six minutes, Joshua delivered his trademark blow to 47-year-old veteran Matt Skelton taking his tally to seven on the trot. Getty Anthony Joshua's career in pictures Konstantin Airich, TKO (3) 1:16 Konstantin Airich became the next victim of Joshua’s brutal run of fights. A third round TKO ended any chance of Airich spoiling the party. Getty Anthony Joshua's career in pictures Denis Bakhtov, TKO (2) 1:00 Joshua claimed the WBC International heavyweight title by destroying Denis Bakhtov in within two rounds showing he is one of the most exciting prospects in world boxing. Getty Anthony Joshua's career in pictures Michael Sprott, TKO (1) 1:26 Joshua needed less than 90 seconds to blast out veteran Michael Sprott and record his 10th successive knockout. Getty Anthony Joshua's career in pictures Jason Gavern, KO (3) 1:21 On this return to boxing, Joshua demolished American Jason Gavern in three rounds, flooring him four times in the process. Getty Anthony Joshua's career in pictures Raphael Zumbano Love, TKO (2) 1:21 Another second round knockout brought Joshua’s up to 12-0 as he flattened Brazilian Raphael Zumbano Love. Getty Anthony Joshua's career in pictures Kevin Johnson, TKO (2) 1:22 American 36-fight veteran Kevin Johnson proved to be no match for Joshua who needed only 2 rounds to walk away with another knock out Getty Anthony Joshua's career in pictures Gary Cornish, TKO (1) 1:37 Joshua stopped Gary Cornish in 90 seconds to win the Commonwealth heavyweight title to the delight of The O2. Getty Anthony Joshua's career in pictures Dillian Whyte, KO (7) 1:27 Joshua battled to beat Dillian Whyte but eventually prevailed with a seventh round knockout, becoming the British heavyweight champion. Getty Anthony Joshua's career in pictures Charles Martin, KO (2) 1:32 Charles Martin hit the canvas twice as Joshua cruises through to claim the IBF world heavyweight title. Getty Anthony Joshua's career in pictures Dominic Breazeale, TKO (7) 1:01 Joshua defended his IBF world title in a seventh round stoppage win over Dominic Breazeale to continue his unstoppable run to the top. Getty Anthony Joshua's career in pictures Éric Molina, TKO (3) 2:02 And then it was 18! Joshua confirmed his tie with Wladimir Klitschko after thumping Éric Molina in three rounds, completing the defence of his IBF heavyweight title. AFP/Getty Anthony Joshua's career in pictures Wladimir Klitschko, TKO (11) Faced by one the greatest heavyweight boxers of all-time Joshua produced an all-time performance, climbing off the mat after being knocked down in the sixth to power back and stop Klitschko with a violent barrage in the 11th round to earn the finest win of his young career Getty Anthony Joshua's career in pictures Carlos Takam, TKO (10) Joshua survived a broken nose in the second round to defeat a valiant Takam, who was a late notice replacement for the injured Kubrat Pulev. Getty Anthony Joshua's career in pictures Joseph Parker, UD The first time Joshua has been taken the distance in his professional career. But he dominated throughout and added the WBO belt to his collection with ease. Reuters Anthony Joshua's career in pictures Alexander Povetkin, TKO (7) Joshua became the first man ever to stop former world champion Povetkin in one of his most thrilling fights yet. Reuters

More than 70,000 tickets have been sold for the fight at the Principality Stadium next week but the event is seemingly now at risk of being cancelled after news of the 36-year-old's muscle strain came to light.

It’s understood that should the fight be called off it will not be rescheduled until spring of next year.