If your knee still isn't better, I wouldn't recommend engaging in any kind of dynamic, high impact exercise. I would warn even more against participating in any kind of sport that involves the knee like football. You will think to yourself that you will just take it easy and have some fun, but it is just too tempting to get excited and competitive, which leads to re-damaging the tissue. Playing football with your friends is the pinnacle of your recovery - you don't get to do it until you are at the end. If improving at or maintaining skill in football is important to you, this could be a great time to focus on technique and strategy, rather than competitive play.
If you haven't been consistent, that's fine - today is the day you can start being consistent for the rest of your life. While having a gym to go to is certainly no panacea for a lack of dedication, it can help a lot with consistency because it can form the basis of creating a habit. Put the effort in to actually show up at the gym every day your training plan says to. If you absolutely *can't* make it to the gym, follow the at-home workout routine already given to you. If you absolutely can't even fit that it, drop on the ground and do push ups to failure - it's not optimal, but it is *something*, and doing something is always better than doing nothing. No excuses for missing a training day.
Your knee, unfortunately, might throw a wrench in things. If you are not fully recovered, you are walking the razor's edge. Strength training has a lot of evidence for helping with injury, but if you go too hard, too fast, you will re-damage the tissue and set yourself back. The key is to apply stress to the injured joint and promote bloodflow to the area, while not going so hard as to not be recovered before the next training session. In the best case scenario, you will be able to follow whatever program you choose as written with no aggravation to the injury, and as you feel stronger you can gradually re-introduce high-impact activity, and then return to sport, letting pain be your guide.
If the exercises prescribed in the training plan *do* aggravate the tissue, then you will need to make some changes - don't be a dumbass and set yourself back just because "the program said to". The point of a strength training program is to make you stronger, not weaker, and when you aggravate your injury, *your are getting weaker*. In this case, you will either need to find a different program, or you will need to tweak the program you are following. Since most good strength training programs use some sort of leg-work as their foundation, it might be difficult to find a program that will work for you out of the box. However, if your knee is only aggravated by squats but not deadlifts, you might be able to find a program that would work.
Making substitutions in a program is never ideal. But if it is necessary, it is better than doing no training at all. When you find an exercise hurts, dropping weight on the lift can help, but if you are dropping to very low weights to avoid pain, it is typically better to simply find a substitution that doesn't hurt where you *can* challenge yourself. Luckily, there are 1000 regressions and variations for any of the common lifts. Try each one you can find until you find something that is both challenging and non-painful. For example, if back squats hurt your knees, you could try subbing front squats, goblet squats, box squats, cossack squats, deadlifts, trap bar deadlifts, romanian deadlifts, kettlebell swings, lunges, reverse lunges, walking lunges, bulgarian spit squats, leg press, leg extension, leg curl, hip thrust, hanging knee tucks, sitting knee tucks, leg lifts, six point rocks, bear crawls, etc. - try anything that at least kinda-sorta emulates the lift you are subbing out.
Let us know how it goes!
