Mets second baseman Wilmer Flores throws to first base during...

Mets second baseman Wilmer Flores throws to first base during the second inning of a game against the Chicago Cubs in Chicago on Thursday, June 5, 2014. Credit: AP / Nam Y. Huh

Infielder Wilmer Flores has been on a tear since he was demoted to Triple-A Las Vegas. By going 1-for-4 Sunday, he extended his hitting streak to 21 games. During the streak, he's hitting .365 with seven homers and 29 RBIs.

But Mets manager Terry Collins said Sunday that a major-league promotion likely isn't in Flores' immediate future.

"I don't want to bring young guys up here and have them sit on the bench," he said. "I just don't think it's good for their development."

Flores, 22, was promoted earlier in the season, though he played sparingly after shortstop Ruben Tejada got on a hot streak.

Said Collins: "If Wilmer Flores comes, I think he's going to have to play someplace, because I don't think he gets anything out of sitting on the bench playing once a week."

Return of Niese

As expected, Jonathon Niese will come off the disabled list to start Monday night's series opener in Seattle. He has been sidelined since July 6 with a left shoulder strain.

Daisuke Matsuzaka will return to full-time relief duty for the first time since May.

To make room on the roster, righthanded reliever Buddy Carlyle was designated for assignment after Sunday's 2-1 loss to the Padres.

Extra bases

Though it was overshadowed by Odrisamer Despaigne's no-hit bid, Mets righthander Zack Wheeler held the Padres to one run in six innings, lowering his ERA to 3.78 . . . Travis d'Arnaud was charged with his ninth passed ball of the season . . . With the designated hitter available to the Mets in Seattle, and with the Mariners expected to start righthanders in two of the three games, Bobby Abreu will find himself in the starting lineup.