Dimitar Berbatov backed Luke Shaw to play for England in the summer.
Luke Shaw is having a superb season for the Red Devils this season.
His lack of consistency paired with injuries made United sign Alex Telles in the summer and this move pushed Luke Shaw to greater heights in his game.
“I thought Luke was man of the match [against City],” the former United striker told Betfair.
“He was great in that game. He was going into tackles, working hard, passing well and playing in a no-nonsense manner.
“His transformation under Ole shows that he has grown into the position.
“I saw a meme saying that since United signed Alex Telles, Shaw has turned into the best defender in Europe. If we put the joke aside, this is what competition can do for you sometimes.
“You feel comfortable, then the team buy someone in your position and you realise that you need to prove how good you are. This then brings the best out of you.
“Competition is certainly one of the factors that has helped him develop and improve. It also comes down to personal motivation, you don’t know about his private life and whether he feels comfortable. He was great on Sunday, as was the whole team.”
The Bulgarian added: “There are lots of good players in both the left and right-back positions for England. Gareth Southgate has decisions to make and he is now the best left-back in my opinion.
“He now just needs to back it up. He just needs to stick to his trends, keep it simple and he’ll be an even better player.
“England have some great talent right now and hopefully Gareth can fit it all together and made a great team out of it.”