A day after placing rookie receiver/punt returner Brandin Cooks on season-ending injured reserve with a fractured thumb, the Saints on Wednesday signed rookie former fourth-round draft choice Jalen Saunders to the 53-man roster, a source said.

The Jets drafted Saunders, who returned six punts for 26 yards over three games for them. New York cut him in late September after he muffed punts in back-to-back games. He turned the ball over to the Jets’ opponent on one of the punts he muffed.

Saunders subsequently spent a total of six games in Arizona and Seattle but didn’t stick with either team or record a statistic. He was on the Seahawks’ practice squad when the Saints signed him.

In a related transaction, a source said the Saints cut running back Brian Leonard, who was in New Orleans (4-6) for one game.

Saunders’ signing indicates that he could audition to handle some of the punt return duties Cooks vacated when he broke his thumb in Sunday’s loss at home against Cincinnati. And Leonard’s departure could mean Khiry Robinson or Pierre Thomas — running backs who have been out injured the past four games — may soon return to action.

The 5-foot-9, 157-pound Saunders returned 20 punts for 308 yards with two touchdowns last year in college for Oklahoma. The diminutive receiver caught 61 passes for 729 yards and eight touchdowns. He ran the 40-yard dash in 4.44 seconds at the scouting combine in Indianapolis.

Saunders joins a receiver corps that includes veteran Marques Colston, second-year pro Kenny Stills (also out of Oklahoma), Robert Meachem (who’s missed a couple of games with a hurt ankle), Joseph Morgan and Nick Toon. The vast majority of the production out of that group comes from Colston (34 catches for 536 yards and a touchdown) and Stills (31 grabs for 431 yards and two TDs).

Cooks, a first-round draft selection out of Oregon State, was second on the Saints in receptions (53), receiving yards (550) and touchdown catches (three), one of which was a 50-yarder. He had also carried the ball seven times for 73 yards and another touchdown when he got hurt and was shut down for the rest of the campaign.

The Saints host Baltimore (6-4) on Monday night.

A day before signing Saunders and letting Leonard go, the Saints acquired rookie safety Pierre Warren from the Vikings’ practice squad and from their own promoted defensive back Terrence Frederick. They also acquired linebacker Moise Fokou.

Correspondingly, aside from Cooks, they placed safety Rafael Bush (fractured fibula) on injured reserve and waived running back Edwin Baker.