Personally, I would use:

Manchester United is still, and will always remain, a strong force despite these setbacks.

Of course, the phrase between the commas can be removed while retaining the original intent of the sentence; however, in this case, the commas tend to also emphasize the idea of 'will always remain.'

I hope you find this helpful.

Personally, I would use:

Manchester United is still, and will always remain, a strong force despite these setbacks.

Of course, the phrase between the commas can be removed while retaining the original intent of the sentence; however, in this case, the commas tend to also emphasize the idea of 'will always remain.'