"Because he hadn't been on the mound is such a long time, he felt a little erratic," Willis said. "As far as going out and competing, one more bullpen [session] will allow him to tighten things up a little bit. On the physical side, he didn't have any issues today."
Willis wants Hernandez to be fully ready when he does return and set Saturday or Sunday in Anaheim as the likely date, if all goes well Thursday.
"He's just played some catch and it's kind of an intermittent thing because he's tried to let this thing feel better, which it is," said Willis. "But he hadn't been able to do anything on the mound, coming down the slope as opposed to throwing on flat ground. It's a little different release point, so it's about repeating that mechanic again."
Hernandez could still potentially pitch in two more games this season, against the Angels and then the A's in Seattle's final homestand the following weekend.
Manager Eric Wedge said Hernandez deserves the chance to finish out the season if he feels 100 percent, even with the Mariners 17 games under .500 going into the Tigers' series.
"There's a lot of respect you have to give him, wanting to finish off the Major League season," said Wedge. "It's a fragile thing, but it's a mighty thing. It means a great deal to finish what you started. He wants to do it for his club, he wants to do it for the game and he wants to do it for himself. And I appreciate all that. He's earned that respect."
With Hernandez still out, Hisashi Iwakuma will start Wednesday's game against Verlander, with rookie James Paxton finishing the series up on Thursday against former Mariner Doug Fister. Erasmo Ramirez will pitch Friday's series opener in Anaheim.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.