Zlatan Ibrahimovic is not fully fit and "made no impression" when he came on as a substitute in Sunday's Manchester derby defeat, ex-Manchester United full-back Paul Parker says.
Since returning for a second stint at the club after major knee surgery, Ibrahimovic has been used off the bench on five occasions, including four times in the Premier League
The 36-year-old, who made his comeback in the 4-1 victory over Newcastle United on Nov. 18, has yet to score a goal or provide an assist this season.
"Zlatan came on at the weekend against City and made no impression at all. He didn't really jump, was beaten in the air, and was beaten to the ball," Parker told ESPN FC at his base in Singapore. "I don't think at the moment that Manchester United fans could say 'great to have him back' if he was to be left out for [Romelu] Lukaku."
Parker, who won five trophies at Old Trafford between 1991 and 1996, is not convinced that the former Sweden international will be able to replicate his 2016-17 form, when he scored a stunning 28 goals in 46 matches, including 17 in 28 games in the Premier League.
"I wonder how fit he really is. He never played any games prior to him coming back to test the knee. Training doesn't do it," he said.
"One thing that he never did [in the 2-1 derby loss to Manchester City] was run in behind, and everyone now is a little bit sceptical about how fit he is at the moment."
Parker added that he hoped that England full-back Luke Shaw would stay at Old Trafford, despite reports that a £5 million payout may persuade him to leave in the January transfer window.
Southampton product Shaw, 22, has made only three appearances this season, and just seven in 2017 after signing a four-year contract in 2014.
"He's working hard, saying all the right things, and he wants to play for Manchester United. I really do believe he wants to prove himself. Otherwise, he'd be shouting and screaming about the manner in which he's been treated [by manager Jose Mourinho]," Parker said.
"It could have been handled better by Mourinho. I believe there should have been a bit of compassion towards what he's had to go through physically and mentally after breaking his leg in Europe [against PSV in September 2015].
"He should be allowed to play his game so people can see how good he can be, in a relaxed atmosphere, rather than being always intense and worried that he's going to be pulled out on the back of a poor performance."
Former manager Louis van Gaal, heavily criticised for his conservative play in two years at the club, described the Mourinho-coached outfit as "boring" and "defensive" -- something that Parker agrees with ahead of Wednesday's home game against Bournemouth.
"Manchester United have to win [against Bournemouth], and they have to win with comfort," Parker said. "It's coming to the point where more people are asking the question: Can Manchester United play expansively? Can they go out and show the style they should be showing, with the players they've got?
"There's no question mark about the players they've got, but they haven't been allowed to show what they've got because it's definitely there."
United, who won the Europa League in 2016-17 after finishing sixth in the Premier League, are 11 points behind Manchester City after Sunday's derby defeat at Old Trafford.