"It's not a minor surgery, and right now the best-case scenario is he would potentially be able to play at some point before the end of the season," Wade said.
Wade said the injury occurred during a cooking accident around Christmas in the Dominican Republic when Vallejo was roasting a pig. Wade said the 23-year-old stabbed the pig with a knife, but he hit bone and cut himself when his hand slid down the knife.
The Astros weren't made aware of the injury until more than a week later.
"We should have been made aware at the time it occurred," Wade said. "He and his agent [Steve Schneider] opted not to let us know at that time. He opted to have it taken care of in the Dominican Republic and didn't let us know. We weren't as front-loaded into the process as we'd like to be. It's unfortunate and we feel badly for the kid."
Vallejo hit .350 in seven games at Triple-A Round Rock after coming over from the Rangers last year and batted .250 for the season with two homers and 38 RBIs between Double-A Frisco and Triple-A Oklahoma City of the Rangers' organization and Round Rock. He batted .275 in the Arizona Fall League.
"We liked what we saw from him here and in the Arizona Fall League," Wade said. "My last day out there [in Arizona], [manager] Brad Mills and I made a point of going out to the clubhouse after the game and telling him we liked the way he went about his business."
Wade said Vallejo's injury won't have any immediate impact on the 40-man roster.
"We have a [Minor League] mini-camp running simultaneously with the opening of big league camp, and if we need an extra infielder we can reach over and utilize a player in Minor League camp," Wade said.
Lyon, who signed a three-year, $15 million deal in December, had a cyst aspirated about two weeks ago, Wade said. The Astros detected a small cyst in the initial MRI before signing Lyon, and his agent called Wade last month and told him Lyon was feeling some discomfort. The Astros flew Lyon in to see team medical director Dr. David Lintner shortly after.
"The follow-up MRI showed it had grown to the size of 1 1/2 grapes," Wade said. "They aspirated the fluid out of it and Brandon went home and began his regular throwing program."
The cyst had been pressing on a nerve and causing temporary weakness, but Wade said Lyon has been throwing without discomfort since the cyst was drained two weeks ago.
Lyon will report to Spring Training as scheduled with pitchers and catchers next week, but because of the birth of his child and the time spent in Houston treating the injury, Wade said the right-hander will be about 10 days behind in his throwing program.
"It shouldn't be an appreciable amount of time," Wade said.