He played in Nippon Professional Baseball (NPB) for the Hanshin Tigers and Fukuoka SoftBank Hawks.

The Boston Red Sox chose Gunkel in the 18th round in the 2013 Major League Baseball draft.

[7] On April 27, 2017, Gunkel was claimed off waivers by the Miami Marlins and was assigned to the Jacksonville Jumbo Shrimp two days later.

In 21 games (15 starts) for the Baby Cakes, he compiled an 8–2 record and 3.20 ERA with 61 strikeouts across 87+2⁄3 innings pitched.

[11] He made his NPB debut on June 24 for the Tigers and pitched 4.0 innings, giving up 3 runs on 7 hits.

[15] In 9 games (7 starts) for the Triple–A St. Paul Saints, he struggled to an 0–5 record and 10.54 ERA with 11 strikeouts across 27+1⁄3 innings pitched.