Why not 1.Nf3 d5 2.c4 Nf6 against the Reti opening? The reply 2...Nf6 to the Reti opening 1.Nf3 d5 2.c4 Nf6 is not even mentioned in my three Reti opening books. What is wrong with that? There must be a well-known answer that is simply part of the professional player's erudition because otherwise this move would get attention from the authors.
This is identical to the position that occurs after the move order 1. Nf3 Nf6 2. c4 d5. The central push d5 is common in many openings, for instance the Grunfeld, but here the timing is bad. The position after

[FEN ""]
[Title "Reti 2... Nf6"]
[Startply "7"]

1. Nf3 d5 2. c4 Nf6 3. cxd5 Nxd5 4. d4


is one I often get with white when I play online, and it usually ends up very well for white. White will follow up with e4 and get an advantage in the center with tempo.

The main difference with the Grunfeld is that there is no white knight on c3 that black can exchange the knight on d5 with, and the knight (and black's whole position) will end up slightly passive.

Sample line:

[FEN ""]
[Title "Reti 2... Nf6"]
[Startply "13"]

1. Nf3 d5 2. c4 Nf6 3. cxd5 Nxd5 4. d4 g6 5. e4 Nb6 6. h3 Bg7 7.Nc3


with a slight white advantage.

Black can also try 4... Bf5 to stop e4 temporarily, but then they have to be really careful. For instance

[FEN ""]
[Title "Reti 2... Nf6"]
[Startply "15"]

1. Nf3 d5 2. c4 Nf6 3. cxd5 Nxd5 4. d4 Bf5 5. Qb3 e6 6. Nc3 Nc6 7.e4 Nxc3 8. exf5!


is very good for white.