After recently vowing to think “outside the box” in constructing his Mets lineup, manager Terry Collins discovered he was lucky just to have a box.

Injuries and slumping players have stung a team that appeared on a roll after winning a fifth straight game, 9-8 in 16 innings, on April 13 in Miami. Since then the Mets are 1-8 and have averaged three runs per game.

They will take a .210 team batting average — which ranks last in the National League — into Tuesday’s game against the Braves at Citi Field and hope the potential return of Yoenis Cespedes can jump-start a sagging lineup. Cespedes has missed the last three games with a strained left hamstring, but indicated to Collins he expects to play Tuesday.

The rest of the Mets’ wounded includes Travis d’Arnaud, who hasn’t started since Wednesday because of a bruised right hand, and Lucas Duda and Wilmer Flores, both of whom were placed on the disabled list last week. Duda has a hyperextended left elbow and Flores incurred a knee infection that left him hospitalized.

And yet, general manager Sandy Alderson doesn’t want to blame the team’s recent slide on injuries.

“We’re just not hitting,” Alderson said. “We’ve had a few guys out, but we should be scoring more runs than we have.”

With the exception of Michael Conforto, the Mets have been without consistent contributors during the nine-game drought. Conforto is batting .361 with four homers and eight RBIs and has brought a presence to the leadoff spot that slumping Jose Reyes (.104) and Curtis Granderson (.171) have not.

About the only thing saving the Mets lineup from complete disaster is its 29 homers, which rank second in the National League.

“It’s easy to push the panic button, it’s easy to say, ‘Oh, s–t,’ but we are too good for that,” Jay Bruce said. “We are a legitimate World Series contender, I believe, and I wouldn’t just say that. This is a team that is stacked. We just have to be healthy and play well.”

As much as Cespedes’ return would help, Bruce doesn’t want the All-Star outfielder rushing back just for the sake of trying to rescue a slumping team. Cespedes may have returned too soon from a quadriceps injury last August, and it ultimately ended with a two-week stint on the disabled list.

“He’s our best hitter,” Bruce said. “Any time you don’t have your best hitter in the lineup it changes it, so obviously he will be welcomed back by everyone, but we have to be smart: A couple of extra days [off] in April is way better than a couple of weeks in August.”

If Cespedes isn’t ready to start in left field, there is a chance he could be available to pinch hit — as was the case Sunday night, when Collins would have deployed him if the Mets had gotten an additional runner on base in the ninth inning. At worst-case, the Mets would like to have Cespedes in left field for their three-game rematch against the Nationals that begins Friday night in Washington.

The Mets will begin play Tuesday five games behind Washington in the NL East after getting swept three games by the Nationals over the weekend, running their losing streak to four.

“There are a lot of good teams in this division,” Bruce said. “Obviously, we understand the ramifications of the Nationals series and stuff like that, but we are playing all division games until May 8, so we are just going to keep playing. It’s a rough stretch right now, but there is nothing to do, we’ve just got to keep playing.”