DALLAS -- Rookie center Dereck Lively II is listed as doubtful for Tuesday's Game 4 because of his sprained neck, but the Mavericks could have another key reserve big man return as they attempt to complete a sweep of the Minnesota Timberwolves in the Western Conference finals.

Power forward/center Maxi Kleber, who has been sidelined since suffering a separation of the AC joint in his right shoulder during Dallas' first-round closeout win over the LA Clippers, has been upgraded to questionable.

Superstar guard Luka Doncic is listed as questionable because of his right knee sprain and left ankle soreness. He has been listed as questionable multiple times during the Mavs' playoff run, but he has not missed any games.

Lively suffered the neck sprain when Timberwolves power forward Karl-Anthony Towns inadvertently kneed him in the back of the head when Lively was falling to the floor early in the third quarter of Sunday's Game 3. He has not entered the NBA's concussion protocol.

Lively, a second-team All-Rookie selection, has averaged 8.5 points, 7.1 rebounds and 1.1 blocks while shooting 65.3% from the floor during the playoffs. The Mavs have outscored playoff opponents by a total of 109 points with Lively on the floor, the West's second-best postseason plus-minus this year, behind only Minnesota center Rudy Gobert.

"We have to have next-man-up mentality," Doncic said after Sunday's win. "Obviously, he's an amazing player. He's helped us so, so much in these playoffs and in the regular season. So obviously we're going to miss him if he can't play. But we got to have next-man-up mentality."

Kleber was a key role player during the Mavs' run to the West finals two years ago and a major contributor during Dallas' six-game victory over the Clippers in the first round, when he made 10 of 18 3-point attempts and played outstanding defense.

His presence provides lineup versatility to coach Jason Kidd, as Kleber is capable of playing center in small lineups that employ a five-out offensive style, and power forward in big lineups.