Robson took over from Neil Warnock in the summer

Robson has already brought in striker Billy Sharp and defender Gary Naysmith, and is said to be still interested in bringing Thomas Gravesen from Celtic.

"I've got a few irons in the fire but there's nothing imminent. I'd like to bring in up to four new players," he told BBC Radio Sheffield.

"I've more or less got to stage where I've got those that I want to stay."

He added: "Now I want to add a few more to the squad to give us a better chance next season."

Robson, who took over from Neil Warnock after the completion of last season, has dismissed reports linking him with West Brom striker Kevin Phillips.