But the 22-year-old was one of the players that looked set to suffer as the Irons made a number of additions to their ranks in the middle of the park over the summer. The increased competition tempted Cullen to seek a late loan move to The Valley.
However, the youngster has insisted that Pellegrini was fantastic with him when he arrived and suggested that he believes that the door on his West Ham career is not closed by any means.
"I thought I needed to be playing and he agreed. I can't thank him enough for supporting me and making me feel at ease. He told me to go out, enjoy my football and improve and, hopefully, I'll return to West Ham a better player for him.
"I would love to play in that team, under Manuel and his staff. It is a good team, a big talented squad, but I know I have to keep working hard every day."
Although Cullen cannot be written off, he is perhaps coming under a bit of pressure as it is rare for academy starlets to turn themselves into important first-team players if they find themselves on the periphery by their early 20s.
There are anomalies, of course, and Cullen has a decent number of appearances for the Hammers first-team under his belt. But his spell with the Addicks could be crucial for his future prospects with his parent club.
The good news for Cullen is that he has featured prominently for Lee Bowyer's side, so if he can continue to remain a key player for Charlton, he undoubtedly stands a better chance of proving a point to Pellegrini.
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