Manager Jang Jung-suk believes the dip in Van Hekken's fastball velocity has been the biggest cause of problems. Never an overpowering pitcher, Van Hekken threw his four-seam fastballs at an average speed of 139.8 kph last year. It has fallen to 136.7 kph this year, and along the way, Van Hekken has also struggled with his fork ball, usually his out pitch that works best when he can deliver his fastballs with authority.

"I don't think he's hurt," Jang told reporters Tuesday before a home game against the Hanwha Eagles at Seoul's Gocheok Sky Dome. "I think he's experiencing trouble with his pitching balance."

Van Hekken held opponents to just two earned runs over his first 12 1/3 innings of the season but then started getting knocked around a bit. The Heroes removed him from the active roster April 26, trying to give him some time to work his way back. He returned for a start last Friday against the Samsung Lions, the KBO's worst club this year, but was taken off the roster again after allowing four earned runs on nine hits in five innings.

At least the Heroes can afford to chug along without Van Hekken. At 19-18-1 (wins-losses-ties) through Tuesday's action, the Heroes are sitting in fourth place, thanks in no small part to homegrown starters who've picked up the slack in Van Hekken's absence.

Choi Won-tae and Shin Jae-young -- along with two former relievers, Cho Sang-woo and Han Hyun-hee -- have gone combined 13-7 with a 2.86 ERA.

If Van Hekken can get back on track in time, he should give the rotation a much-needed shot in the arm in the dog days of summer, when inexperienced starters like Cho and Han could tire.

Van Hekken experienced similar issues last year. He actually left the Heroes to sign with the Seibu Lions in Japan to start 2016. But unable to get his velocity up to his usual level, he was just 0-4 with a 6.31 ERA in 10 games before getting released.

The Heroes welcomed him back in July, and Van Hekken quickly went back to his normal self, winning his first five decisions en route to a 7-3 season and a 3.38 ERA.

And Jang is hoping for a similar turnaround this year.

"If he gets his command back, I believe he will be as good as last year," the manager said. "We'll wait for him if he needs more time."

The Heroes are trying to reach their fifth straight postseason, and they will need a healthy and effective Van Hekken if they get there. He has a 3-2 record in eight postseason appearances with a 2.18 ERA. (Yonhap)