Sky Sports understands a number of clubs are tracking highly-rated Carlisle United midfielder Brad Potts.
Sheffield United are planning to send Andy Butler back out on loan after seeing an agreement with Walsall collapse.
The 34-year-old has agreed terms with Blues and passed a medical but the club are waiting on a visa application before a one-month deal is completed.
Former Senegal international Diop, who helped West Ham to promotion to the Barclays Premier League last season, has impressed on trial at St Andrew's.
He has also played in England for Fulham and Portsmouth, with whom he won the FA Cup in 2008.