Kevin Molino, Eric Miller doubtful to play Saturday for Minnesota United

Two days after he left a friendly against Hertha Berlin because of tightness in his hamstring, Minnesota United midfielder Kevin Molino didn't train Friday and coach Adrian Heath called him "doubtful" to play against Houston on Saturday.

Molino was just coming back into form after knee surgery early last season when he left Wednesday's game late in the first half.

"With hamstrings, it's all these little things that come along and you just don't want to push him," Heath said. "We've got a big month coming up, and he's got a big month with the Gold Cup coming around the corner with training. It's important he's 100 percent fit … We don't want to take those chances."

Molino is set to play for the Trinidad and Tobago national team in the Gold Cup at Allianz Field next month.

Neither Molino nor defender Eric Miller were on United's Friday injury report, but Heath called Miller (quad) doubtful to play Saturday. United also has just loaned midfielder Romario Ibarra to a team in Mexico.

The Loons worked Friday to refine their set pieces. They've had some discrepancy recently about who'll take their corner and free kicks — star Darwin Quintero or designated specialist Jan Gregus — and just where they'll go.

Asked if they have corrected things, Heath said, "We hope so. We know where the ball should go. We know where people should be. It gets frustrating. The quality we put in the box this morning going over it was unbelievable. We need to consistently get that on match day."

When asked who'll take the kicks, Heath firmly said, "Jan will be taking them."

San Jose's Chris Wondolowski waited seven months to surpass Landon Donovan as MLS' all-time goal scorer. When the moment finally came last weekend, he didn't just score once to tie Donovan's 146 goal total. He scored four times in a 4-1 victory over Chicago.

"Good for him, man, he's earned it," said United veteran defender Ike Opara, a former Earthquakes teammate. "I was telling someone about the trajectory of his career, and I don't think they understand the work he put into what his career is now. He did a lot of grinding his first four, five years, but he got his opportunity and never looked back. He's one of the great soccer stories in this country."

Seattle's three-time MLS Defender of the Year Chad Marshall played the final game of his illustrious 16-year career at Allianz Field this month. He retired suddenly Wednesday because of a degenerative knee joint.

"For me, he's one of the best center backs in MLS history," said United's Ozzie Alonso, Marshall's Sounders teammate for 10 seasons. "It's very sad he had to walk away, but it's life. I'm very pleased and very proud of everything he did in Seattle."

JERRY ZGODA