Depending on how ambered the finish is, its probably going to require bit of tinting. Which usually takes a professional to get it just right, but if you are patient and willing to experiment you can usually get pretty close.

So you will want to sand the area with 100grit paper, hand sand, no machines.

then apply one coat of polyurethane straight. no tint. let that dry.

scuff the area with 150-180 grit, clean and apply a second coat of poly. this is usually where i will try to tint. you will probably want a yellowish tint. not bright yellow, more a darker yellow.

since the area is small...get a dixie cup, fill about halfway with poly, and litterally only 1 drop of the tint. mix well and apply a light coat, and this is where your eye has to come into play. take a look, if its not enough tint, add one more drop...Only add a drop at a time, the tints are powerful and can become wasted if adding too much (hence why only using a dixie cup too)

once you think you got it, let it dry and then ever sooo slightly scuff a little bit, not too much or you will remove the tint. then add one more light coat of regular polyurethane. make sure you feather out the strokes to help blend with the existing floor.

you may notice the repair for a little while but after normal traffic hopefully it will blend nicely.

Good advice. I have two things to add. Putting on a clear coat first as gregmills recommended is important. If you put on tinted poly and it's not right, you can wipe it right back off. When you tint poly, it seems to dry a little darker than when it's wet. Use minimal tint and do multiple tint coats if needed. It's better to sneak up on the right color rather than getting it too dark and having to sand it back off after it dries.