More on both of their injuries will be determined on Thursday.
Mitre, projected to be one of the top three starters in the rotation, will throw off flat ground at 60 feet on Thursday. The right-hander experienced tightness in his right forearm on Feb. 29, when he was pitching against the Orioles in Fort Lauderdale, Fla.
In the first inning that day, he faced three batters and exited with his sore arm after just 15 pitches. He has been on no-throw status since, although he has been conditioning and doing other drills.
Maybin, the 20-year-old center fielder, also was hurt on Feb. 29 in a split-squad game against the Nationals in Viera, Fla. He felt tightness in his left hamstring while running the bases in the ninth inning. He was removed from that game for a pinch-runner.
Maybin did more intensified running on Wednesday. The plan is to get him into the game either Thursday or Friday.
"Thursday maybe, and definitely by Friday," manager Fredi Gonzalez said when asked about Maybin's return.
Maybin is a highly regarded prospect who is competing for the starting job in center field. The setback has caused him to miss five days of games.
It's still early enough in Grapefruit League action for Maybin to seriously battle for a starting position. But the Marlins are closely monitoring the gifted prospect, who was obtained from the Tigers in the Dontrelle Willis-Miguel Cabrera trade in December.
Maybin said he has never experienced any leg troubles, and he is feeling better by the day.
If he is held back to Friday, he would be ready to face the Nationals in Jupiter.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.