Steyn, who missed last weekend's victory over Australia due to an ankle injury, will undergo surgery on Wednesday and is set to be out for three months.
"We've been doing a number of scans and seeing specialists, there is quite few loose bodies in the joint, little pieces bone that in time has broken of ankle," said Roberts.
"Every now and then bones catches into the joint and gets excruciating pain, it can damage the joint.
"It was taken as long term decision, he will be done (operated) on Wednesday, unfortunately keep him out for three months, also for end of year tour."
Young fly-half Johan Goosen sat out of training on Monday because of a bruised heel while full-back Zane Kirchner also did not train due to a bruise on his hip-bone.
"He (Goosen) was comfortable running (on the field), just when he planted his foot for kicking," Robberts said.
"We always knew beforehand that he may be sore, which is why early on we decided to change kicker."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.