PITTSBURGH -- Right-hander Chris Archer is making progress as he works his way back from the injured list to the Pirates’ rotation.

After throwing a bullpen session on Tuesday, Archer is scheduled to test his right thumb by pitching in a simulated game on Friday at Busch Stadium in St. Louis. Director of sports medicine Todd Tomczyk said the Pirates will determine Archer’s next step after that.

“He continues to trend upward and make steps to getting back to competition,” Tomczyk said.

Archer has been on the injured list since April 27 due to right thumb inflammation. He tried to pitch through it and allowed six runs over four innings on April 26 at Dodger Stadium. With Archer and Jameson Taillon sidelined by injuries, the Pirates put Steven Brault into their rotation on Tuesday night and started Nick Kingham on Wednesday afternoon.

Archer could be back relatively soon. The Pirates will have to fill Taillon’s spot for a while longer, but his second opinion from Dr. David Altchek confirmed Pittsburgh's initial diagnosis of a right elbow flexor tendon strain. Taillon will be shut down from throwing for approximately four weeks, then he will have to rebuild his arm strength before pitching in games again.

Update on Burdi

After seeking a third opinion, the Pirates finally gained some clarity regarding reliever Nick Burdi's mysterious arm injury. Tomczyk said the root cause of Burdi’s right biceps pain is a nerve injury, which caused him to crumple to the ground in extreme pain after throwing a pitch on April 22.

“That complex set of nerves was stretched and compressed to a point where it just caused that excruciating pain in his biceps,” Tomczyk said.

Tomczyk added that the Pirates are not concerned about Burdi’s forearm, flexor mass or reconstructed ulnar collateral ligament. Doctors did not recommend surgery for Burdi, but they advised he rest for six weeks after the injury -- so, approximately four more weeks -- before he attempts to throw again.

“What Nick is dealing with is a nerve injury, an acute neurogenic nerve injury,” Tomczyk said. “This will take time.”

Roster moves
The Pirates placed reliever Keone Kela on the 10-day injured list, retroactive to Monday, due to right shoulder inflammation. Kela had not pitched since exiting Saturday’s game, but he remained on the active roster until after Wednesday’s 9-6 loss to the Rangers at PNC Park. The club announced that it would make a corresponding roster move, likely adding a fresh arm to a taxed bullpen, before Thursday’s series opener at Busch Stadium.

Outfielder JB Shuck, who was designated for assignment on Saturday, was outrighted to Triple-A Indianapolis after clearing waivers.

Trainer’s room

• Outfielder Lonnie Chisenhall (left calf strain) should be ready to run the bases soon, which means he is nearing the start of another Minor League rehab assignment. Chisenhall has not played this season due to a fractured right index finger and, more recently, a mild calf strain.

• Left fielder Corey Dickerson (right posterior shoulder strain) is ready to resume playing catch after being set back by tightness in his throwing shoulder. The Pirates reassessed Dickerson’s shoulder strength and range of motion on Wednesday morning, but there is no timetable for his return to the field. Dickerson has been on the injured list since April 4.

• Shortstop Erik Gonzalez, on the 60-day IL with a fractured collarbone, had his stitches removed on Wednesday morning and began a “gentle” running program. Tomczyk said Gonzalez is on track in his recovery.

• Catcher Jacob Stallings, on a rehab assignment with Triple-A Indianapolis, should catch back-to-back nine-inning games soon. Stallings, out with a cervical neck strain, began his rehab assignment on April 27.

• Triple-A right-hander J.T. Brubaker is dealing with “a little irritation in the back of his elbow,” Tomczyk said. Brubaker will avoid throwing for at least another week before being reassessed.