It's very clear from the first two games of the Premier League season that Manchester United's summer signings have strengthened the team, but there are still a few areas where Jose Mourinho will be looking to improve before the transfer window closes.
The pursuit of Ivan Perisic suggested another winger was on the wishlist, but left-back is also an area of uncertainty as neither Daley Blind nor Matteo Darmian have made the position their own while Luke Shaw is clearly someone the manager hasn't got much faith in yet.
There have been rumours that the club considered a move for Danny Rose, but another name that has been linked in recent months is that of Celtic star Kieran Tierney. John Hartson still has a close connection to Celtic and the former Welsh international was speaking on BBC's Scottish Football Podcast when he revealed that he was informed that Tierney was Man Utd's top priority in the transfer market.
I’m hearing he’s Manchester United’s number one target.
But why on earth would Brendan Rodgers sell Tierney right now?
If I’m Brendan Rodgers, Im saying to Mourinho, ‘Let him have another season here, keep your £25-30m for now, he’s got Champions League football, he loves playing for Celtic.
If Kieran Tierney has another season, if he’s outstanding in the Champions League, playing really well against the top teams, in the spotlight, all over the world being looked at by the top clubs.
Celtic fans are unlikely to be worried, as it's blatantly obvious that Kieran Tierney is in no rush to leave the club he loves, but Hartson is correct to say that if the Scotland international impresses at the highest level once again there will be interest in him that will be hard for him to turn down.
He's been slated as a future Celtic captain for good reason, he already conducts himself as if he is and leads by example on the pitch, but it may get more and more difficult for the club to hold on to him as he continues to improve.
You can listen to Hartson on the Scottish Football Podcast over on BBC.co.uk.