Declan Rice trained with West Ham United on Tuesday.
The midfielder has seen Arsenal and West Ham agree on a British record 105n fee.
Both clubs insist Rice will join Arsenal, though final details are yet to be signed off.
The Sun says the hold-up now stems from Arsenal lawyers combing through the wording of the deal before giving it the green light.
In the meantime, Rice has begun training with the Hammers as he waits for the deal to be settled.