Alexis Sanchez's imminent arrival at Old Trafford can turn Manchester United into serious contenders for the Champions League this season, former Red Devils striker Norman Whiteside has said.

Arsenal forward Sanchez, 29, is scheduled to undergo a medical on 21 January ahead of his move to Manchester, with Henrikh Mkhitaryan moving in the opposite direction in a straight swap deal.

United are in second place in the Premier League – 12 points behind leaders Manchester City – while they face Spanish side Sevilla in the Champions League round of 16 next month.

Whiteside described Sanchez's signing as a major coup for United and backed his former club to go far in Europe with the Chilean forward in their ranks.

"City have got to win the title from here – but after signing Alexis Sanchez I can also see United winning the Champions League," he told the Sunday Mirror.

"Sanchez is a special player who can make the difference in the biggest of games and he's been desperate to get away from Arsenal so that he can join a club that's going to challenge for the top trophies.

"United have already got a manager who has won the Champions League against all the odds before.

Alexis Sanchez
Alexis Sanchez is poised to become Manchester United's highest paid player Getty

"If the European Cup came back to Old Trafford then that would put City back in their place."

Sanchez is reportedly poised to be United's highest-paid player with weekly wages of £400,000 ($550,000), and Whiteside warned that the club's other big-name players could demand pay rises to match the Chilean.

"The one thing I do know about footballers is that they talk about money," Whiteside said. "They talk about it in the dressing room before training, after training, on the team bus.

"And the deal that Sanchez is getting to join United will be one of the main topics of conversation amongst the players because they will now want a piece of the action."