MILWAUKEE — Now the Mets will hold their collective breath and hope Steven Matz isn’t facing a significant layoff.

Matz was sent back to New York on Sunday for an examination because of what manager Mickey Callaway described as a “nerve issue” in his left forearm that prevented the pitcher from throwing a side session.

Matz underwent surgery in August 2017 to decompress and reposition the ulnar nerve in his left elbow, but Callaway said it’s not believed this situation is related. Matz last pitched on Friday, when he allowed three earned runs over 5 ²/₃ innings in a loss to the Brewers. According to Callaway, the left-hander has dealt with irritation in the forearm during recent starts.

“He has been battling it for about two weeks now, has been able to pitch fine and swing the bat fine,” Callaway said after the Mets’ 3-2 loss to the Brewers. “But at this point when it was bothering him today we figured we better get it checked out.”

Matz is scheduled to pitch Wednesday in San Diego, and Callaway indicated a Plan B hadn’t been decided. Candidates for the start would include Corey Oswalt, Drew Gagnon and Chris Flexen.

Matz’s departure from the team came on the same day Jason Vargas departed early with left hamstring discomfort. The Mets could skip that spot in the rotation until May 18 if they choose because of built-in off days.

If Matz is sidelined for an extended stretch, it would heighten the need for the Mets to more aggressively pursue starting-rotation help from outside the organization. Dallas Keuchel remains the biggest name on the free-agent market, and the former Cy Young Award winner has remained on the team’s radar, according to an industry source.

Matz has been the Mets’ most consistent starter this season, posting a 3.86 ERA and 1.20 WHIP in nine appearances. Jacob deGrom and Noah Syndergaard appear on the rebound after recent slumps, and Zack Wheeler has been solid, but except for one ugly start against the Phillies last month, Matz has shined.