The 21-year-old midfielder tried to head clear in their FA Cup third-round match with the Shrews – but he was met by a high boot from Abu Ogogo which kicked out two front teeth.
Horrific video footage showed the moment one of the Republic of Ireland Under-21 international’s teeth flew from his mouth as blood poured from it.
He received treatment on the pitch while the tooth was picked up by one of the West Ham medical staff. Cullen played on – without the teeth – and his battling spirit was praised by boss David Moyes.
He said: “Josh was probably our best player. Considering he’s only just come back and we’re getting to know him, he did well.”
Moyes will now decide later whether to keep Cullen and Reece Burke, who both featured against Shrewsbury, at the club or allow them to return to Bolton on loan.
Rules state that players on a season-long loan can be recalled by parent clubs in the January transfer window if a recall clause has been agreed in advance.
They now can’t go out to any other club – meaning a choice between regular football at Bolton or boosting the squad at West Ham.
Moyes also has a decision to make on whether Joe Hart can leave West Ham to secure first team football and rescue his World Cup dream.
Hart is a on a season-long loan with the Hammers from Manchester City, where Pep Guardiola has told him he isn’t wanted.
Hart started the season as first choice goalkeeper under previous Hammers boss Slaven Bilic.
But he has not featured in the Premier League since losing his place to Spanish rival Adrian at the beginning of last month.
Hart’s axing and the impressive form of Adrian has resulted in an upturn in results for the Hammers.
Hart kept a clean sheet in Sunday’s goalless draw against League One outfit Shrewsbury Town in the FA Cup third round after being handed a rare chance by Moyes.
But he still faces a desperate battle to win back his place full time and fears this could see him miss out on Gareth Southgate’s England squad for the World Cup in Russia this summer.
He could now push to leave West Ham early so he can guarantee regular game-time with Newcastle also interested in taking him.